Have been searching for a kind of table/ list/ overview of all possible beasts sorted by highest Con relative to CR levels. This obviously has to do with what beasts are better for going into battle while having highest probability of making the saving throw for maintaining concentration on spells.
I've never seen that. I'd suggest that you put it together yourself with only the beasts that your druid has seen on it. If I was going to put something like that together my list would be greatly different than your list anyway because mine would only include the beasts I'm able to change into.