To clarify, it is a dildo. If I can find an actual plug that's 10-12", has enough girth that I'm going to feel the pressure but not so much that it's impossible, it flares out and then narrows at the base suitably that it is easy to retain, and also has a comfortable base, that would be perfection. Unfortunately, I suspect that the people who design them aren't the same as the people who use them.
As for your other question, Astroglide does work pretty well. I also have some generic gel stuff from the drugstore that works well too. I'll apply just enough to the head and that ends up taking care of the whole thing, surprisingly enough.