I found post op my back size went up, mostly I think swelling and have continued wearing for comfort, but they are too big. I got a couple of bras in M&S yesterday and they’re def not my right size, I had to muck about a bit with the sizes as well, I got a maternity bra (!) in 36DD – v comfy – and 2 non underwire padded bras in 36D, backs are too big so the cups feel a bit roomy but am hoping when I can wear proper bras I will be able to buy a better size back. Also I wonder if because the implants are so round they don’t fill an entire cup, natural breast tissue would automatically fill the cup through natural movement, I would just keep trying on bras until you find one that fits. I made the mistake of buying without trying and now have 11 no underwire and sports bras that I’ll prob never wear. They’re going on ebay!