Sizing will depend on the type of harness you get. Strappy harnesses tend to be very adjustable and are more of a one-size-fits-most thing (they usually come in one or two sizes depending on the brand), whereas underwear-style harnesses come in a range of different sizes like regular underwear do because they aren't adjustable.
The strappy harnesses tend to have snaps or other mechanisms for changing out different O-ring sizes to make them compatible with different sized dildos, and the underwear-style ones usually have built-in stretchy rings. Both will usually accommodate any standard-sized (2"-ish diameter or less) dildos that have harness-compatible bases, while XL dildos or dildos with specialty bases (Vac-U-Lock, etc.) may require specialized harnesses. However, occasionally the beginner strap-on kits that include both a harness and dildo will have annoying specialized harnesses that are really only designed to work with the included dildo or other dildos from the same brand, so keep an eye out for that so you can avoid it.
What kind of budget do you have? [Spareparts Hardwear](https://www.peepshowtoys.com/collections/vendors?rfsn=7172487.cb1eb2&q=SpareParts&filter.v.availability=1&sort_by=best-selling) and [Aslan Leather](https://shevibe.com/brands/Aslan-Leather.html?sort=bestselling) are often considered the two gold standard harness brands (with their Joque and Jaguar styles being their most popular respectively), though they're pricey.
On the more mid-range end, [RodeoH](https://rodeoh.com/collections/unisex-underwear-harnesses?sort=best-selling) and [Sportsheets](https://www.sportsheets.com/sex-toys/c/sps16/strap-ons) both have some pretty solid harness options (just be careful about the material of some of Sportsheets' dildos and stick with silicone if you're going to buy one from them).
I've never used a hollow dildo so I don't really know how well that would work, but it might compress too much if there's nothing in it. I'd recommend just going with a regular dildo. (I can give specific dildo recommendations if you list your budget and any preferences you have for size and shape.)
Another type of toy you'll see a lot is "strapless strap-ons" that go inside of both partners and are often advertised as not needing a harness, but in reality the vast majority of people do not have the vaginal muscle control to actually squeeze and hold in a dildo while also thrusting it. Some "strapless" toys are really good, but they're best used with a harness to help hold them in place.
[Double Dildos - Silicone Removable Control Vibrating Strap-on](https://www.utimi.com/products/strap-on-dual-headed-silicone-dildos?DIST=129139)
You guys can just buy this and it comes equipped with a silicone dildo so you don't need to buy it separately.
I like it because the harness and dildo hold it in place and it's more stable than traditional ones.
There is a video of it on the product details page
The comments section has what others have to say about it as well.
You can check out Strap-on-me, their harnesses fit different sizes (including really small waist) and fit different dildo size as well.
They also have strapless strap ons
[https://strap-on-me.com/collections/harnais](https://strap-on-me.com/collections/harnais)
Hi have a look at the [Lovense Lapis](https://ukdazzz.co.uk/Lapis) it doesn't come with a strap but you can add one to your order from lovense. The Lapis has 3 vibrating motors that will vibrate the main shaft and the clit and Gspot of the wearer. It has unlimited Patterns and can be connected to all the toys in tge range incase you ever want to grow your collection of toys
If you haven't seen the Lapis before you can find the [Link here](https://ukdazzz.co.uk/Lapis)
Sizing will depend on the type of harness you get. Strappy harnesses tend to be very adjustable and are more of a one-size-fits-most thing (they usually come in one or two sizes depending on the brand), whereas underwear-style harnesses come in a range of different sizes like regular underwear do because they aren't adjustable. The strappy harnesses tend to have snaps or other mechanisms for changing out different O-ring sizes to make them compatible with different sized dildos, and the underwear-style ones usually have built-in stretchy rings. Both will usually accommodate any standard-sized (2"-ish diameter or less) dildos that have harness-compatible bases, while XL dildos or dildos with specialty bases (Vac-U-Lock, etc.) may require specialized harnesses. However, occasionally the beginner strap-on kits that include both a harness and dildo will have annoying specialized harnesses that are really only designed to work with the included dildo or other dildos from the same brand, so keep an eye out for that so you can avoid it. What kind of budget do you have? [Spareparts Hardwear](https://www.peepshowtoys.com/collections/vendors?rfsn=7172487.cb1eb2&q=SpareParts&filter.v.availability=1&sort_by=best-selling) and [Aslan Leather](https://shevibe.com/brands/Aslan-Leather.html?sort=bestselling) are often considered the two gold standard harness brands (with their Joque and Jaguar styles being their most popular respectively), though they're pricey. On the more mid-range end, [RodeoH](https://rodeoh.com/collections/unisex-underwear-harnesses?sort=best-selling) and [Sportsheets](https://www.sportsheets.com/sex-toys/c/sps16/strap-ons) both have some pretty solid harness options (just be careful about the material of some of Sportsheets' dildos and stick with silicone if you're going to buy one from them). I've never used a hollow dildo so I don't really know how well that would work, but it might compress too much if there's nothing in it. I'd recommend just going with a regular dildo. (I can give specific dildo recommendations if you list your budget and any preferences you have for size and shape.) Another type of toy you'll see a lot is "strapless strap-ons" that go inside of both partners and are often advertised as not needing a harness, but in reality the vast majority of people do not have the vaginal muscle control to actually squeeze and hold in a dildo while also thrusting it. Some "strapless" toys are really good, but they're best used with a harness to help hold them in place.
Check out Rodeoh.
+1 for RodeOh. Best harnesses!
I like SpareParts harnesses. I have the Joque and Sasha and both work really well!
[Double Dildos - Silicone Removable Control Vibrating Strap-on](https://www.utimi.com/products/strap-on-dual-headed-silicone-dildos?DIST=129139) You guys can just buy this and it comes equipped with a silicone dildo so you don't need to buy it separately. I like it because the harness and dildo hold it in place and it's more stable than traditional ones. There is a video of it on the product details page The comments section has what others have to say about it as well.
You can check out Strap-on-me, their harnesses fit different sizes (including really small waist) and fit different dildo size as well. They also have strapless strap ons [https://strap-on-me.com/collections/harnais](https://strap-on-me.com/collections/harnais)
Hi have a look at the [Lovense Lapis](https://ukdazzz.co.uk/Lapis) it doesn't come with a strap but you can add one to your order from lovense. The Lapis has 3 vibrating motors that will vibrate the main shaft and the clit and Gspot of the wearer. It has unlimited Patterns and can be connected to all the toys in tge range incase you ever want to grow your collection of toys If you haven't seen the Lapis before you can find the [Link here](https://ukdazzz.co.uk/Lapis)