Hammocks can be tricky with hammies as they chew things. Here are my suggestions.
Rat sputnik (not quite a hammock but they seem popular with hamsters if they hang next to shelf so they can get in easily - with a bit of bedding in).
Tunnels & Dens: Sputnik Hanging Den | Small pet accessories at zooplus
Zooplus also sell this grass hammock. It's not too bad but can have some sharp woody bits so needs checking. I was allergic to it - lol. It smells very grassy.
Trixie Natural Grass Hammock for Pets at zooplus
Erin's hamsters has a hammock made out of toilet rolls on this video. You'd need to use sisal string though rather than cotton string, in case it gets chewed. I like that one
https://www.youtube.com/watch?v=NuPeyD6w-CI
Vectis had a great hammock made from a cardboard egg box type thing
(Scroll down page to see hammock) - again best to use sisal rope.
Managing Bar Chewers
Someone on here tied a chill and chew mat to the cage roof at the corners to make a hammock
https://www.amazon.co.uk/d/Small-Ani...l+and+chew+mat
Don't use cloth hammocks though - the threads, when chewed, can get tied round teeth or legs and cut circulation off leading to amputations. Also don't use chains to hang things up because little feet can get caught in the links and hammies end up hanging by a broken leg.
Fleece hammocks (if well made and without stuffing) are sometime used but this is only suitable if your hamster doesn't chew it. Slightest sign of chewing and it would need to come out.
I tried our last Syrian with a fleece hammock as he wasn't a chewer but sure enough he tried to pull it to bits (anything soft they think is good for nesting material so they try and chew bits off to pouch). But - once he was quite old I was able to put a fleece snooze cube in his cage because he was too old to be bothered to chew it and his teeth weren't up to it