As someone who had to have a gastrocnemius recession, I feel your pain. The flex of your feet are controlled by the soleus when sitting and gastrocnemius when standing. To save you a horrific search, my tendons are too short and had to be lengthened.
I still go on my toes if I am trying to balance or the tendons aren’t quite warmed up yet in the morning. Standing with my heels down for long periods is still not comfortable, but I can at least walk around all day without collapsing. Not the same thing, but I get the being on your toes being comfortable.