As others have mentioned, salary matching would play a big part here. You could go for somebody like Sabonis, but his contract ends when Jaylen's does and I'm not sure his ceiling is as high as Jaylen's.
I don't see it likely, but there were a number of solid bigs in last year's draft (Ayton, Bagley, JJJ) that would have an additional 2 years left on their rookie contracts. I can't imagine any of them would be available for Jaylen straight up, but it's not like we are short on picks to offer.
There is always the nuclear option of Tatum/Smart/picks for Towns, but I don't think he is available.
More likely, we stick with our wing heavy line-up and see if Tatum/Brown can take off.