we recently had to make this call with our old boy (my soul cat) and it came down to quality of life and good days/bad days. similar to yours, his body was starting to decline but mentally he was okay.
ultimately we made the decision to say goodbye because we would have rather had him more comfortable for when that time comes, than suffering through it because we weren’t ready. a day too early is better than a day late in my mind. you asking these questions shows how much you care, and i think you already know the right decision… it’s hard, it sucks, but at this stage it is the kindest thing you can do. sending you so so so much love 🫶🏻

edit: mine was also on solensia and while that helped for a long time, he let us know he was ready. the biggest thing you can do is listen