Oh boy that one sounds a bit rough. I honestly would have avoided the island swamp in the first place, it's hell trying to land a boat in a swamp without some chaotic BS like that happening to you. But since it's already a bit late to take the "eh, i'll find another one" route since you eventually want to recover that stuff you lost, let's see if anyone can help find a solution.

Troll armor should indeed be enough, and for the time investment that bronze takes it might not be worth making that for the extra like 8 damage protection unless you just plain have abundant bronze already (i personally hate bronze age so this is never the case for me, i get exactly what i need to move on to swamps and 0 of anything I don't NEED to do so). If you do happen to have more bronze than troll since you've been funnelling your troll kills into armor upgrades for armor you are currently trying to get back, then yeah, the bronze might be the easier loadout for getting your stuff back.

This one might be one of those "we'll get it later" recoveries though. It also sounds like you got a death cycle bad enough that you simply wont be able to properly prepare to recover your stuff before your skill drain protection is gone, so rushing the recovery will probably just make your situation even worse. Take that time to remake another troll set or a new bronze set (whichever is more reasonable based on what resources you still have, if back to square 1 both will take time anyway). If that swamp is a full island, with absolutely nowhere safe to land on it, then it may indeed be best to set up a forward base with a portal on an adjacent landmass (you did mention more land across a smaller canal, if that lands offers meadows or even black forest somewhere nearby that may be feasible). that forward base wont get you back to your corpse, but can at least get you back into the area from a safe nearby location, plus you can use it to try different approaches to that swamp.
A land bridge across the canal with a hoe would probably be the safest way to cross the leech infested waters over to swamp island, but if that isn't possible it might also be worth considering finding one of the large ancient trees on the shoreline you can toss a workbench down on top of (safely out of enemy reach, they cant wreck the giant trees) and use that as a "landing" so you can try a raft approach. Leeches will decimate boats if given the chance, so it might not be the worst option to bring the materials for 2 nice cheap rafts, one to get there and one to get back if the leeches ate the first (but you already have the resources so you arent wading through shallow leech waters trying to find the bits of the first raft they broke, these are meant to be disposable rafts for the sake of recovery basically).

If all else fails, there are players willing to help with moments pretty much exactly like this. As in there are groups dedicated to helping players recover from deaths they can not reasonably recover from themselves. You might be able to reach out to one of them and have someone join your game to help you get your stuff back.