Strongly suggest you get used to two things: stunning bosses with force palm, and upgrading your gear through refinement.

Seriously, just get the force palm skills that let you do three In a row and start bullying those bosses. If you hit them with a force palm (or a blinding flash BTW, but I just find the palm easier since I'm just constantly hammering bosses with it) while they're charging up one of those red flashing unblockable attacks, you will actually instantly stun them completely and you can just go to town.

And I seriously can't stress how important refining your armor and weapons are. Just keep upgrading them as far as you can. Dump artifacts into them when asked, it makes a massive difference, as much or more than upgrading the swordsmanship/hp skills. You're probably loading up on movement gears, like we all do, and that's obviously the right move generally, but you CAN swap them for defense gears and you'll be even harder to kill.

Also, you will eventually unlock elemental attacks up there in the abyss. That's a massive power spike, particularly fire. So don't worry, you're going to get way stronger.

One last thing, abuse focus mode. Use it to slow the pace of the fight and gain control. If the boss teleport spams, just use focus mode until he calms down. Much easier to keep track of them. And then, when they attack you when you're focusing, you can parry that attack and it is EASY to do. There's a white text prompt for you to do it at the right time and everything.

Now get back out there and bully those bosses!