Those two positions are obvious but a forward-thinking team would also look to add to the DL if possible.
Lawrence is the only elite pass-rusher on the roster and the 2nd and 3rd best pass-rushers are unreliable off the field in Gregory and Irving. Collins, Crawford, Charlton, etc. are ok as complementary rushers but if you have to rely on them to be your top guys you're in trouble, and that would pretty much be the case if Lawrence were to miss time.
I'd look hard at guys like Frank Clark and Grady Jarrett, they will command big time money but you have to take a chance at some point and there's nothing wrong with spending on top players in their mid-20's, especially when they could take an already very good group and possibly turn them into a dominant one.
Sign Earl Thomas at a discount, break the bank on a Lawrence extension and either Clark or Jarrett, and you're looking at a unit similar to the 2015 Broncos that could carry a team to a Super Bowl.