look for rootstock Emla-111 or otherwise bud-118. 111 preferred. Largest of grafted stock that does Well in clay type soils, etc. doesn't root sucker much, doesn't usually need a massive amount of staking to keep up, high volume production, etc. longer to produce but a far better tree long term- no question.
I'd look at some pollinating crabapple varieties to add to ur rust resistant trees and also do a few varieties. I go heaviest on Arkansas black, enterprise, Yates, liberty, freedom, limbertwig, empire, etc. I do have my reasoning and spraying routine to do pink lady, goldrush, etc as well. Heck- all apples need some care & watching but not horrid.