Well for a start, I'd certainly ignore the passenger comments.
For a start, as you well know, passengers have no idea about the situation, nor what actually makes a good landing. I've had passengers compliment me on the best landing they've ever felt after slamming it on, and conversely had people say it was a bad landing when it was as good as I've ever felt. Many really have no idea.
If you were floating, and looking like landing long on a short strip then the place to be is either on the ground, or going around. Who cares if its a bit firm? We're not talking hard, damaging the aircraft... just firm. You're safely on the runway, and decelerating... not chewing up valuable runway.
The thing I think you need to ask yourself is: Do you have confidence that you can put the aircraft on the runway in the touchdown zone repeatably? If the answer is yes, but sometimes its going to be a bit firm, then you've got nothing to worry about. Runways with slopes can be a prick. Just keep doing it. If the answer is no, and you don't have confidence you can put the aircraft where you need to, then you need to go back to basics, and get that right before worrying about smooth touchdowns.
I think sometimes we get caught up in the theory of it all. When it comes down to it you know where the wheels are, you know where the runway is... so just visualise putting the wheels where you want them, and do it.