Well done on approaching the surgeon, first of all - it isn't easy to pluck up the courage and that's a huge step.
Sorry to hear what they said. It must be a bit of a blow. It was a good idea to get a second opinion, though, and it sounds like the second guy was a bit easier to talk to. How long ago was your surgery? I'm surprised to hear you still have staples. I assumed they'd have come out long ago.
If you're still keen to give it a go then as the surgeons said only you can decide and have to weigh up the risks. I'd echo what they said: be very, very gentle, use lots of lube, and start with a finger. You've had the end of a colonoscopy up there so obviously that's not going to do any damage.
If that's possible, then you're already doing great, and fingers are perfect for prostate simulation. There are all sorts of small toys out there, too. It's not all about genital penetration.
And if it's not possible, then I wish you luck, and will say what I've said before: penetration need not be what gay sex is about. Many people don't enjoy it and choose not to do it.
Good luck x