Are you using any enemy cards? Some of them could be useful, like Creeper Plant, which is a leaf bracer, and will let you use your Cure cards, even if broken.
Also, like other people have said, don't use sleights. In the enitrety of the battle, I probably used sleights maybe... twice, but I also had a card that recovered all of my attack and magic cards that I used, too.
There's no use trying to jump and attack her face until you get rid of the tentacles that are slithering around you. Slice away at the tentacles until she reels back in surprise. You don't even need to get rid of all of them to be able to get to her.
Also, use Mickey's card when it turns up, because that get rid of a lot her HP in one go. Also, take the time to heal. I would put your cure cards at the end of your deck, instead of scattered through the deck. That way, it doesn't take as much time to find them, especially when you just reloaded.
Ursula isn't really that hard, in either the original game or the remake, so perhaps leveling up a couple more times will be of use to you. You might not be leveled up enough, if you're only able to use 25 cards.