You might think about the catacombs for the extra estus if you're dying a lot at sens, although it can be bitch to climb back out of there afterwards. If you're at a level where the snake men are really tough, parries and backstabs will be the best way to deal with them. If that doesn't suit your playstyle, you may have to go back to old blighty to get enough large shards to make your uchi +10 so you can hurt em good. Don't forget dex is the base stat for uchi, it's damage is connect to how high your dex is, you wanna get dex to around 40. If that's not appealing, you may have to cheese them with arrows, for example poison arrows, or many of them can knocked off of things by headshots with arrows, which knock enemies back. This is certainly a consideration when dealing with the lightning shooting serpents above you but it depends on angles, poisoning and patience might be better.
Killing Hydra is also a great task for where you are currently at, it will seem too easy later. Did you meet Dusk before? Once you kill hydra, quit and reload, then wade into swamp looking for a gold golem
No time to stick around, but I agree that taking out Havel for his ring is a great idea, it is one of the best rings in the game along with ring of favour and protection and hornet ring, which is acquired in the forest area you mentioned earlier.