On my Macbook Air I have been running Sierra 10.12 for a while now, recently I wanted to use Drafts on my Mac. To do this I needed to update to High Sierra (10.13).
I did not want to go Mojave, I know a few people have said that the Mac was running fine, but as soon as they upgrade to Mojave, as they had slightly older hardware then the performance is seriously affected.
It’s not easy to find the link to go High Sierra as they want you to upgrade to the latest version. If you do want this the link to this is https://apps.apple.com/gb/app/macos-high-sierra/id1246284741?mt=12
This may allow you to upgrade without having to jump to the latest.