@Scandimandy
Re cushions, I just shoved a pillow from the spare bed down there when I had to go in the car after my reconstruction! It worked fine, even if I did get some strange looks from people giving me a lift.
For sleeping, I didn't need any other support, but needed to be slightly further into the bed so the drains (I think I had 2 for the mastectomy and 3 for reconstruction) could rest comfortably on the bed. Sometimes a long handled, little cotton bag worn round your neck can have your drains in is helpful - the hospital gave me one kindly made and donated to them for this purpose. It saved me getting tangled when getting up in the night for the loo. You also need to get used to sleeping on your back for a while, which was difficult for me, and a nightmare for my husband as I snore. Loudly, apparently 😴😂
Re the bra - I was a 34g/GG, but dress size 18 and I found Sainsbury's front zip up in large was perfect - please allow for a bit of swelling pot op. In fact, I started wearing these when I had my mastectomy (delayed reconstruction) in lockdown, and I've never stopped as they are so comfy! I only tolerate a sports bra when training - comfort is more important to me now 😁
I hope some of this helps, and that you are happy with the results x