What are the best hardcore survival mods or mod pack(s)? I want a true survival experience unlike vanilla Minecraft where I can have a full set of diamond armor in the first 20-minutes of the game and pretty much be invisible. Also I would like for there to be a mechanic where the player's health reacts to the weather. I you have any recommendations please post them. Vanilla Minecraft has gotten quite stale for me. Thanks!
For mods on their own, both MITE (Minecraft Is Too Easy) and Terrafirmacraft aim to make the vanilla survival experience fairly difficult. MITE doesn't play particularly well with other mods, but Terrafirmacraft will at least coexist with a few. Enivromine, Hunger Overhaul, and Spice of Life also either add realistic mechanics to minecraft or make basic survival that much harder.
The only mod pack I can think of offhand that's made to make survival really difficult is Eyamaz's Blood N Bones pack on FTB.