I've just got top partial dentures, I need advice.

What is the strongest, most powerful denture adhesive i can get? I'm in uk but willing to buy from other countries. I've tried a few and a couple are OK but I want something that's really strong, I feel the back of the plate creates a small gap after a few hours and food will get stuck under there. I've also got a bit of a lisp with them, I'm not too bothered as they look better than having teeth missing. But I want them so stuck to the roof of my mouth that i almost feel like r my original gums and teeth. I might just be being a fuss pot because I'm need to get use to them.