First of all bravo! The fit and finish on this topper is unreal. The attention to detail is second to none.
In regards to mattresses, we went the cheaper route, milliard, and have no regrets. It's firm and even when kneeling I don't bottom out (200lbs).
There are tons of adhesive backed options out there for gaskets. If you have a local supplier nearby, I would recommend stopping in and asking to see everything they have. Hard to beat putting your hands on a product to make sure it's what you want.
Can't wait to see more pics, keep up the great work.