The lance would be a good weapon to try if you've been using the knife. It's got a shield too, so the play style isn't all that different in essence.
I dunno, they strike me as being pretty divergent; the Sword and Shield is about quickly darting in and doing a fast combo, and quickly getting out of range. The shield is a fail-safe (since a lot of attacks breach the shield). I actually think the Longsword player would be most comfortable using the Sword and Shield.
The Lance on the other hand is more conducive to making your own opening in the monster's defenses, nailing a body part, and then bracing for the counter-attack. All the other weapons are about keeping distant from the monster's attacks, while the lance generally works best when the monster's always close by and prime for the counter. The lance is also trickier than most weapons because it changes how you move about most efficiently, especially when it comes to closing modest distances and in cancelling the (massive) cooldown its attacks have.