I honestly don't entirely remember how I playtested my game to make sure every jump was do-able, the development process is all a blur now. I know I tried to keep the controls relatively easy and made the map layout more forgiving for the player as well as myself. I think I had some ideas for obstacles in mind but generally managed to build the majority of the map from the ground up in just a handful of revisions.
I did drag the player in the editor window to certain parts of the map when I needed to test or practice certain sections but also tried doing a full run through of the game every once in a while. When working on the final jumps and ending to my game I dragged the player up to a position I knew could get to and just went forward from there.
I didn't stress too much on raising the level of difficulty as you climbed higher in my game, I more so just raised the stakes. My ultimate rationale though was that if I could do it then you could too, and I think it worked out pretty well.