"I wish there were," or "I wish there was," which sounds most natural? [duplicate]

There are two questions that need to be answered here.

First, is there still the slightest chance that there is something I can do for you? For example, I might think that there is probably nothing I can do for you, but I still need to think about it a bit before I can be sure. In that case, I'll say "I wish there was something I could do for you."

Second, how formal is the language you're using? If there is absolutely no chance that I can do anything for you, and I'm speaking formally, then I should say "I wish there were something I could do for you." If there's no chance at all that I can do anything for you, and I'm speaking in a neutral or informal register, then I can use either was or were.