Yeah that whole health bar shrinking thing, and the difficulty in finding something to fix that, is almost incomprehensible to me. I get it, make the game difficult, but that just feels like a cheap and quick way to make the game feel difficult without actually working on ways to make it interestingly so. Like BB which is hard without resorting to cheap tricks. It makes it a lot more rewarding.
But you'd hope that since BB was made after, they'd have learned how much better this approach is, and fixed it on DS3.
I still feel like a total noob playing DS2, no matter how much I blame the (bad IMO) design of the game. People played it, loved and finished it, so what's wrong with me??
Get the Mace. It is very strong due to its strike damage. Then get craftman's hammer.
Get a heal miracle, to help you in longer runs.
Get an item that increases your endurance regeneration and health generation (can be found quite early)
Get the ring of binding to keep you health var at 75%.
Start using a shield at first (you can block an astounding amount of attacks throughout the game.
Note that it is much stronger to upgrade the weapon, instead of relying on its scaling. I typically just put as many points in dex and str needed to use the weapon.
Make sure to level up adaptability. This increases your agility. Agility is super important, as it determines the number of invincible frames when you role.
You can farm areas and make enemies vanish (after 10 times, they disappear)...this helps you not only in increasing your soul level, but in clearing the path to bosses.
This tipps should get you started, later infuse your weapon with an elemental and increase the stat that scales it.
Note, you can also respec in DS2, so you can try out many different builds and playstyles...