One thing that I have noticed, and this is probably old news to mostly everyone, is that when I am struggling with a boss it's usually because I am trying to block with my shield too much. A lot of the times when I just suck it up and go two handed, it forces me to learn the boss' attack patterns and how to properly dodge them. I am not saying you need to drop the shield entirely, but doing a few attempts at a boss without even trying to use your shield will FORCE you to learn the dodge timings.
Also, dodging towards the boss and trying to circle around them seems to almost always be a better option than dodging away from them. Also, not getting too greedy and just settling for one light attack during your attack opportunities can help conserve your health.
But yeah, as others have said, there is so much to do and explore that it's not really worth it beating your head against the wall trying to beat one particular boss. I am about 40 hours in and I think Margit is still the hardest boss I have faced thus far. Everything else has been way easier in comparison.
Once you level up your health, stamina, weapons and flasks the game's combat will become a lot more lenient. You won't usually die to just one or two attacks anymore. Although, if you play like shit you will still get destroyed by even the basic enemies in the game, lol.