You've got a few options but it basically boils down to stacking poison resists and having purple moss to cure poison. How you go about it is a matter of preference. Dark Souls is kinda old school RPG in that there's A LOT of emphasis on the items/gear you pick up versus character skills/spells/stats. It's all about finding a weapon/gear piece and then taking it through a particular upgrade path at a Blacksmith versus finding various versions.
Reccommended gear:
Shield - Spider Shield or Heater Shield
Gear - Whichever you prefer. Then ninja gear is light armor and has high poison resist.
Rings - Ring of Favor and Protection is a game changer especially if earned early (it boosts raw + Max Health and Stamina )or the Wolf Ring (it boosts Poise - the stat that keeps you from going into hitstun when attacked). Rusted Iron Ring helps negate movement penalties running through water so yeah, it could help in the swamp but isn't critical.
Recommended items:
Purple Moss Clumps - Without a doubt, these are invaluable since they cure poison. You can buy them from the
female undead merchant in the tunnel shortcut to Undead Burg or you can farm them from the plant guys on the path to Darkroot Garden.
Honestly the easiest thing to do is just make sure you have plenty of Purple Moss Clumps and Estus heals and not worry about stacking resists from gear if it's a huge pain to get. That way you can get poisoned and be able to recover once you've made it through the swamp parts and can move normally. Congrats on getting that far, Blighttown can be a bitch early on and you're almost at a pretty tough Boss fight. Let me know if you need more help.
