I personally only beaten the game with Jill, I never got to finish chris but I did try it once and had to stop right away once I noticed he has less inventory space then jill (LIKE A WHOLE LOT LESS...)
I heard he can take more damage before he goes down though... but I also heard all the items are replaced in different areas as well and it will be like playing resident evil 1 (1996) for the first time again.
I finished both campaigns, in the original game as well as the remake, and it's true that Chris has more health and less inventory space ("a whole lot less" is pushing it, but yeah, you'll definitely face more backtracking with him). Most of the important items are found in the same locations, it's just that some are exclusive to one character (like the bazooka to Jill), and some require different methods of obtaining depending on who you're playing as (for example, Jill can get the shotgun early by having Barry save her from the ceiling trap while Chris will have to look for the broken replacement no matter what, he also has to find small keys to open drawers that she has a lockpick for). So yeah, it won't be 100% the same, but not completely different either.
I don't know why everyone say that Chris is harder, but I had personally died more frequently whit Jill because of the few healt she have, sometime she can only deal two hit from zombie, while Chris can take many hit, making the game easyer in my opinion...
The remake balanced out the difficulty of the campaigns a little by adding the lighter as Chris's personal item (he didn't have it by default in the original RE1, but it wasn't so important because you didn't have to burn corpses), toning down the usefulness of Jill's lockpick (which back in 1996 could also open sword key doors, not just locked drawers), and giving Chris a unique self-defence item that outright kills zombies (Jill's taser
can be lethal too, but it's not guaranteed). Still in both versions, Chris never gets his hands on the bazooka, leaving the shotgun as his primary weapon against bigger enemies, he has a smaller inventory, doesn't have Barry to save him from danger, and can't mix the V-JOLT by himself which actually allows Jill to completely skip the Plant 42 boss fight. These are some of the reasons people generally find Chris's campaign harder.