First of all...welcome to the site.
The newspeedmaster seat is much smaller and less supportive than your stock seat. It's low-profile and the way it's made is there is about 1/2 to 3/4 of an inch of some very hard foam, topped with about an inch of very soft foam which crushes down to the hard foam and does not add support. The seat is good for less than 100 miles. Then forget about it. This is only my opinion and I do not believe the Newspeedmaster seat is an upgrade in feel...just looks.
If you want a good, COMFORTABLE seat, go with the Corbin. It's the most comfortable I've sat on and I have had a lot of seats: Stock America, Stock Speedmaster, Stock Touring, Corbin, a couple of my own low-profile seats that I make, and the Newspeedmaster Low-Profile.
The Corbin will provide you with plenty of area to sit on, it's contoured, and it's firm. It's the best.
If you want to just firm up your seat, you need to get it re-covered with some thick, heavy leather and it will change it quite a bit. Other options is to send your seat to get some new foam. Some other guys could chime in about that.
