i've read that the JJ2 plus addon can add more higher possibly wider resolutions but also that it does not work with the 'LK Avalon' version of the game. Apparently this is the version you get from GOG. Any alternate suggestions?

GOG includes JJ2+ as a goodie, and you can update it to the latest version on Jazz2Online.

It's a bit confusing but the answer is that GOG cheats. They distribute the LK Avalon version because it's technically the most recent official release of the game, in that it adds a (not very good) Polish translation that other JJ2 releases didn't have. But if you tell GOG to switch you over to JJ2+ (e.g. by using the Beta Channel feature in GOG Galaxy), then that swaps out some of the main files, meaning you're not actually running LK Avalon anymore, and that's why JJ2+ is suddenly able to work.