You can lubricate the cup with water before inserting (just dunk the whole thing). Never tried a personal lubricant on it, but I wouldn't think most of them would interfere with the seal.

If you're not allergic to latex, there's also The Keeper. That's what I had until my dog ate it. I replaced it with a Diva Cup, which for me, never sealed as well and as comfortably as the Keeper.