stick with what you have, they are the stadard size for a 110, 90's are nomally lower, but will take 235/85 or 265/75 without mods.
265/75 is the standard for alloys when sold new.
Spend the money on things which will give more benefit in the short term and wait until the tyres wear out before deciding which way to go. If you do change from 235/85 you will also have to change the rims, so the costs keep mounting.
I'd buy some diff guards, steering guards, snorkle to start with.