Only way to go slow, and more stable is to change design types...
Pretty much ALL centerboard monohulls will feel slower, than your cat... but they probably are LESS stable (I know counter intuitive).
Want REALLY stable? pick a tri-maran.
But honestly what you might want to consider is a swing keel boat, or really ANY keel boat.
Want a real stable 18 foot, monohull? Sorry I link to this only to show you what one looks like not to show you an ad - Victoria 18. Victoria 18 sailboat for sale
It also has really nice lines.
Capri 18, Compac 19, Precision 18... Compac 16, Precision 165... these will be stable trailer sailor 16-18 foot boats... ALL of them will feel like slugs compared to a Hobie.
Nothing wrong with going to keelboat to get some stability for sailing.
The Buccaneer, is a really fast centerboard boat, but I wouldn't call it "stable." Nor is a lightning, or thistle, or any number of other small centerboarders. Don't get me wrong these are great boats to learn on, but you have to acknowledge that they can capsize, and that is part of the learning. If you want something that likely won't ever capsize, again, go keelboat.