I know that this will be an unpopular response, but it really depends on you. You know your limits. If you are totally and completely able to fly the plane without struggling with orientation then you can step up to whatever you want pretty much. I would avoid warbirds with heavy wingloads and jets maybe as second planes, but anything else should be more manageable than one might think. Scale aerobatic planes are not that hard to fly, as long as you keep a little speed on while you are learning to land.

If you are really doing what you are saying you are doing, then you should be able to fly any of the 60-90 size knockaround sport planes with no problem at all.

I went from a Kadet Senior, to a U CAN DO, to a pattern plane and a 30% Edge 540T in less than a year. Not bragging but there is nothing that says you have to go to a gentle flying second plane, there is not that says you don't. If you are absolutely wringing out your trainer, flying it like its borrowed and have no trouble getting out of awkward orientations then you will be able to handle just about anything.

If you are struggling with orientation at any level then just stick with trainers and work it out. But don't avoid doing things that make you uncomfortable, go after them. If you struggle making right turns then do nothing but fly right turns for a while. You have to find your defiencies and work through them