I had a single mastectomy 5 years ago (and getting the other side done now in a few weeks). I used one of those foam wedge pillows since I didn't have a recliner either. It worked well enough until I was comfortable and healed enough to sleep flat on the bed.
I bought a triangle/wedge style pillow to elevate my leg and help get the swelling down (since this places my knee above my heart when I lay down - or even sit up slightly).
I think the concern with normal pillows pillows is that if you place them under your knee only your leg rests in a semi-bent position. I have found that the wedge is pretty comfortable and it supports my extension. If I feel like I need a little extra support under the ankle I also roll up a little hand towel and place it there to let gravity help amplify the extension.
For background I’m F/5’2” and I got ACLR with a hamstring autograft (reinforced by allograft) and repair of a Bucket Handle Tear of my Medial Meniscus on Monday (3/14). Because of this I am locked in extension (totally straight) for what may be the next 6 weeks and am only ok’d to bed my knee to 90 degrees with no weight baring right now. Prior to surgery my meniscus tear made it impossible for me to straighten my leg so keeping those extension gains are important to me!
Here is the exact pillow I got. I told my PT & Surgeon about it and they both said this was great.
https://www.amazon.com/dp/B004X7CBDA?ref=ppx_pop_mob_ap_share
I bought this wedge for $29, was super happy with it. It's stiff so I put two pillows on it and slept pretty good. https://www.amazon.com/dp/B004X7CBDA?ref=ppx_pop_mob_ap_share
You'll have to experiment with your positioning and communication. First: communication. You will need to be able to tell him when he's getting too far in, and he needs to be able to hold back on the thrusting a bit.
Next: positioning. Some large, firm pillows of various shapes should allow you to combine them to make a customized cushion to take the weight off your hips. For example, this wedge pillow might be helpful:
Well! As I was writing this, I googled "sex pillow," and here's what I found. I'll bet this would help:
Sofa cushions and/or accent pillows are firmer than bed pillows, and come in a wide variety of sizes. You can find them in many discount home supply stores, but do put them in a pillowcase: