Good luck my friend. Hollow Knight is a special one, but those bosses can be punishing. A few of them took me separate sessions over a few days, which is a frustrating way to play games for me, but it's such a rewarding experience otherwise. I recently rewatched my recording of beating one of the bosses and I was fumbling so bad, I could see my own desperation in the way I was playing.
Apparently there's a secret phase for the final boss that I was more than happy to experience via YouTube. I was perfectly satisfied with just rolling the credits.
Hollow Knight is the greatest game of all time for me. I replayed it recently and it was such a different experience for me to move through confidently and quickly when I had a grasp of combat from the beginning. It took me months to finish it the first time because of getting lost and not knowing where to go next.
Some generic (no spoiler) tips:
go in another direction and come back to the boss later if that's possible. If a boss is way too difficult then there may be an upgrade you haven't gotten yet.
take your time. It is more important to save your health rather than rushing to get a hit in. Sometimes it's worth going to a boss and not hitting him at all and just focus on learning movement, patterns and figuring out where the openings are.
play around with your charms and get the best setup you need to help with the boss fight.
try to avoid attacks by running into the gap in projectiles rather than relying on dashes all the time.
if you're coming to thinking of quitting the game based on difficulty, then there's no shame in watching a boss guide video on YouTube. Or space it out with a secondary game so you can play something else and come back later.
Possibly. The very early part of the game is linear. Very quickly in this game you'll find it impossible to look up a guide because it is so non-linear, and it is really difficult to judge where you are in the game because you might have done things in a completely different order. Generally, early bosses just take a bit of practice and pattern recognition, and tend not to be reliant on upgrades.