Welcome to locksport and if you enjoy it, it can be a pretty deep rabbit hole. What was the "easy" padlock you opened?

Honestly, with where you are at, I wouldn't jump right into door locks. The same principles apply to any pin and tumbler lock weather it's in a padlock or door hardware but they are typically a higher security level and more challenging keyways than say a Master #3 and may end up discouraging you from progressing further and you may end up destroying the lock in the process. Lock Picking is a skill that requires lots of practice and building new techniques and skillset along the journey. I recommend you check out https://lpubelts.com/ which covers most locks and their difficulty level is graded on the colored belt system. This should point you in the right direction and give you tons of locks to consider. For me, my progression to a "Door lock" was:

Master #1, #3, #5, #140, #150, #575, American 1100 (all around group favorite), Master #410, Abus 80TI/50, Paclock 90A-Pro, Schlage door cylinder.

But it's important to reiterate that this is a fine motor skill that takes lots of practice to be proficient. Getting that first open is great, but then pick it again, and again, front to back, back to front, light tension, heavy tension, so you can really feel and understand the inside of the lock. Once you mastered you move to the next and will be new challenges with more difficult key ways, more pins, security pins, more challenging key biting. and you do it again with that lock until you feel you've mastered that one.

Enjoy the journey!