Hi mower
My ds2 had open heart surgery at 9 months old too. Unfortunately, his surgery was an urgent case, so we were admitted just 4 days after getting a full diagnosis and surgery was 3 days later. I too was very worried about breastfeeding, but was able to breastfeed him a little closer to the time of op as breastmilk is more easily digestable. I then pumped while ds was in surgery and in intensive care. I found it quiote stressful so made sure I had a photo of him and something that smelled like him to help with let down. I also never got on with the hospital grade breastpump, so if you have one, perhaps take your own? Anything I pumped went to PICU first and got put down his feeding tube very slowly, like 1ml an hour. A few hours before we left PICU, ds went absolutely balistic (morphine comedown maybe?), it took several nurses to keep him on the bed. In the end, they said that I could try breastfeeding him as he took alot of comfort from that. It worked like a charm and 10 minutes later he was in a deep sleep! Ds2 was also very much the mummy's boy, a very unsettled baby and the only thing that worked to some degree was floor walking of breastfeeding, so I KNOW where you are coming from when you talk about how much contact you have with each other al day, everyday.
We also were not given much advice on picking him up after surgery, but some kind of instinct kicks in and I found myself scooping ds, like a newborn, rather than lifting under the arms. It was a few weeks before I felt comfortable to do that again.
The good news is, kids bounce back pretty quick. Although ds was very ill by the time he had surgery, he was in PICU for just over 48 hours, HDU for 12 hours and came home 6 days post op!
Saggar has already suggested Heartline, which is a wonderful board. If I can help you in any way or offer any more advice, you can have my email address if you want it.