As previously mentioned by others, the 1st overall just doesn't get moved very often. It would likely take a lot to get it. You're not getting that pick for players making large salaries in this environment, when the player picked at 1 is going to provide solid value on an ELC.
Even if the Jets got it, and really don't need another winger, I could see them taking Laf if no big offer comes along. A player like that on an ELC is a huge thing.
For me to move it, I'd want #3 for sure to draft a C, an unprotected 2021 1st round pick, and a 2022 1st round pick. Possibly add a clause that in 2022 if the Jets finish higher in the standings (and draft later), the picks are swapped. If the Sens finish higher the pick goes to the Jets.
Gives the Sens a big win on draft day 2020 (1st, 5th, the Isles pick, and 4 seconds). Sens would need to use cap space (owner I know) to improve the team to make the next 2 drafts not hurt as much.
Jets would get a C in the pipeline that they need, and possibly a D in 2021 as there seem to be a lot of good D available. 2022 is a wildcard.