CASM - Cipscis' Automatic Save Manager by Cipscis
This is mod that has finally made it's way over from Fallout. I've been using for FNV so long I can't remember a time it wasn't installed. It's saved me so many headaches over the years and now it's finally here for Skyrim.
Basically, install it and setup up your autosaves accordingly in the MCM menu and forget about it. Easy peasy.
I haven't actually tried the Skyrim version yet, but if it's anything like it's FNV counterpart then this is a shoe in for STEP. Never will I forget to save again after running around for 2 hours and not saving.
Options include autosave frequency between 1-30 minutes, amount of autosaves to use, and toggle saving during combat and sneaking.