Sam Darnold went for a 2nd round pick, and a 4th... if you trade Fields, I feel like you have to at least get a 2nd.
There's probably not a trade out there for #1 that makes me feel it's worth it, because you just have to fix QB. The rest of this roster is on the verge of competing (assuming they can fill WR, C, DT and the smaller gaps through FA/picks) if they can get a QB in there to have an above average offense.
I would be tempted, if the Bears own pick lands at 5 or 6, to move down to 15ish and add a 2nd rounder... add a defender like McKinstry, Newton, Latu, Chop Robinson, Jared Verse, etc. and then a WR with the 2nd rounder