I have no idea how to help you, and to be quite honest I find this style really gross. (the massive diapers larger than the person wearing them, etc) Not trying to hate on you or anything, its just not my style.
That being said, I would love to see more chara/frisk diaper/omorashi art. If you look up "diaper/omorashi/pee/etc" + "undertale" 95% of what you get is skeleton porn. I just really don't get it. why draw skeletons in diapers/peeing when you have two perfectly good humans who are living in a world that literally has no toilets.
I would love to see less exaggerated diaper art of one or both of these two. I can post what little I have here if you want, as well as the even rarer omorashi/pee stuff.