Stop trying to bring your heel up to your bum, and stop doing heel bends in bed to a level of 4-5. These things are not necessary to have improvement.My bend of heel to bum is tough. I do heel bends in bed with a band but only go to pain level 4 or 5. I do this a few times a day.Doing stairs is tough as well. At 5 months is this OK to be at this stage.
Stop doing stairs foot over foot, since that is still tough. Wait a few weeks and try again. If it’s still tough, wait some more and try again.
I had the same issues at 5 months that you do. Your knee is not yet even halfway healed, and pushing these things is not helping it.
All you need to do at this point is your daily activities, try to relax (which I know is very hard, I was very worried my whole first year) and give your knee time. I cannot stress the time thing enough.
If you really want to do exercises, these are the only ones you need:
Extension: how to estimate it and ways to improve it
Heel slides and how to do them properly
I wasted way too much time worrying about my ROM the whole first year. I had a lot of improvement in my second year as I continued to heal and my whole leg continued to relax.