I want to go walking in the pool
well I'm pretty sure you'll need to NOT do any swimming at all for at least 8 weeks, too much strain on the sternum.
After that the skin will be healed and the skin is the primary barrier to infection. So you should be fine.
I'm going to say you should be doing walks every day, a few times a day from the first day out of hospital.
I don't know what your valve choice is, but I'm going to say (having known you here for some years now) that you should pick a tissue valve, I'll venture that the Edwards Resilia is probably the best bet. At your age it should see you out. Especially given your anxiety levels you are psychologically not a good candidate for a mechanical NOR managing your INR properly.
Best Wishes