You can probablymay be able to protect allies from your skin while using Touch-range spells on them.
But you'll need to ask your DM.
Based on that, it's probably safe to assume that your character does not actually need to come into skin to skin contact in order to use Touch-range spells.
That leads to the last problem, which is the big one...what is "direct contact?" Well, grappling only requires one free hand, so you can 'grapple' by grabbing someone with a gauntleted hand. The fact that a grapple always causes a save against a Grung's poison means that their poison can apparently affect you straight through the glove of your gauntlet.
Based solely on this...anything that lets you communicate a Touch spell would also potentially transmit your poison. But the phrasing of "comes into direct contact with your skin" leaves the possibility of things like shoving a Grung into a burlap sack and not getting poisoned through the sack. So--if the Grung is wearing clothing, does it protect you from their skin? Is the special case with grappling because thisyou have to grab and squeeze to hold them in place, so their poison is pressed through your glove?
All-in-all, the fact that it calls out a requirement to either grapple or come into direct contact with a Grung's skin leads me to believe that if a Grung wore clothing and was not handled roughly, the clothing would be able to contain their poison. This would allow you to physically contact party members in a clear rulingway that would allow Touch-range spellcasting, without poisoning them. At the cost of preventing you willfrom just touching enemies to poison them unless you took your gloves off first.
If you want to check withbe absolutely certain/safe...then grab the Ritual Caster or Magic Initiate [Wizard] feats to get access to Find Familiar, and let your familiar do all the touch-range spellcasting for you.
This is far from a concrete ruling--you will absolutely need to ask your DM about this--but hopefully, this post gives you some discussion points you can bring up with them.