This is really something that should be built-in from the beginning IMO, with the option to disable it on easier difficulties. Bolting it on afterwards is going to make things difficult.
That said, I really like Frostfall plus Realistic Needs and Diseases in Skyrim, and damage really should be increased in most Bethesda games as standard, though this going to make melee builds really difficult to play, as a single mistake can already get you killed in the vanilla game against harder opponents.
Not sure I like the idea of only being able to save when sleeping; as others have said, regular saving is crucial in Bethesda games, not least of all because it lets you avoid various quest bugs or the random deaths that can occur by stumbling upon a high level enemy unexpectedly.