Just tossing around scenarios if we really wanted to go "all in" for title contention-
1) Trade Mitch, Fournier, 1st round pick (and possibly additional picks) for Ayton. We love Mitch, but we know his limitations. His hands are rough, he doesn't finish as well as he should, has no range outside the basket and can't make free throws. Ayton is as good a rebounder, has more scoring talent (can make FTs and hit an occasional jumper) and has shown signs defensively. However he's a softy, inconsistent, a coach killer etc. However for the price he'd probably the be the easiest upgrade in the middle we could find.
2) To really go all in, follow up with Barrett, Rose (team opts him in to salary match) and Rokas for DeRozan. This is truly a win now move. DeRozan is not a shooter, but he plays the the Barrett role with more efficiency/consistency and is a proven clutch performer. Bulls get the younger player, that helps them re-set without downgrading that much talent wise. They get DRose's curtain call and a prospect in Rokas.
Knicks field a lineup of DeRozan-Randle-Ayton-Brunson-Grimes. Hart, Quickley, Hartenstein, Toppin, McBride on the bench. Its a pretty strong team with DeRozan adding some playoff/veteran moxie and Ayton is no stranger to the playoffs himself.
BUT...if you really want my opinion, I prefer to stay the course- just think the above is something that is do-able and puts you in a close place.