Hmm... I think for SHM expert mode (abbreviated to ESHM from now on) you'd need something to reduce damage by a flat amount in order to make it so you don't get 2 hit by everything, melee/tank classes might not have too much of an issue but mages, summoners and rangers would all suffer greatly from a single hit without decent damage reduction.
If i remember correctly, in the 1.2 version you could make a slime talisman that made you immune to slimes and reduce damage by 20%, perhaps making a new recipe for that that uses royal gel then combining that with the worm scarf/frozen turtle shell to give 40% damage reduction would be a good idea? The biggest problem though is that it might become an essential accessory (much like the inertia boots) and/or become too OP for an already tanky player, I know tanks have the titan gauntlet which combines the paladin shield, mechanical glove, frozen turtle shell etc. so maybe just make a slime talisman/worm scarf combo for the other 3 classes to combine with their top tier accessory but only make it craftable at a SHM anvil.
Last idea I have for doing it this way is ESHM only treasure bags for at least the 3 starter bosses (EoC, EoW/BoC and Skeletron) and make the unique item each 1 of 3 parts (much like the mechanical minecart) to make a 'catalyst' for combining a damage reduction item with a high tier accessory for each class.
Or the most simple thing could be make an upgrade to the inertia boots that uses 1 or multiple damage reduction items, but that's no fun is it?
EDIT: Oh right, forgot to mention I couldn't use the nebula wings to make the inertia boots in version 10.5 or this version, I can only assume that it is the same for the other 3 tower fragment wings.