I'm approaching a year and a half since I threw away my mach 3, and I still have my good days and my bad.
for anyone who tells you to shave with a straight only, and not to use your DE
They are giving you bad advice. You can't master straight shaving in a day.
use your straight to get as much as you can comfortably, and finish with your DE, eventually you will not need the DE, but for now, a comfortable enjoyable shave is most important. Use the tool that works best for those difficult areas.
You will learn faster, and develop better techniques this way.