I know what you mean, I don’t like the U/U either.
Did you try and suggestions in this thread to try and establish which ingredient is causing the reaction? The difference between vanilla and U/U is the vanilla flavouring and the sucralose sweetener. It sounds like you are going to need a something sweet in there to mask the taste of U/U but it doesn’t have to be sucralose.
If you can establish if you have the reaction with sucralose first and then we have something to work with.