Booggie
you could give him an adapting/improving body (not to op thought) like the more he gets hits with stunning,cuttung, ect spells the less they affect him or that he is constantly getting stronger by a small margin and has no limit. ex: by that start of avengers if he did nothing to improve himself he would have the body of a super soilder and more magic then voldemort and by endgame he would be as strong as thor in avengers (so thanos would still beat him easily) this is if he doesn't train at all. and if he does ... I'm mainly going for this since you could focus more on Harry's life then him just getting stronger all the time. like have him make some friends.. ps. just saw the new Dr strange movie... wanda needs a happy ending(family) and so does harry... (wink wink) plus pietro seems like a cool guy in the movie(for what little screen time he got)