That's a tough question - when I first read your requirements, my first thought was to suggest a hardware synth, since those are truly, "turn on and play". With Ableton, Logic, Pro Tools, Fruityloops, Reaper, Maschine, Reason, Cubase, and so on, there's no way that manufacturers could make a controller specific to each, which is why (in 1987) Mackie and Digidesign created the "Mackie Control Universal" standard, which helps a great deal by mapping physical to virtual control surfaces with visual feedback, motor control, and so on. The downside is that each manufacturer has to create and maintain a mapping setup, which maps their control surfaces with to a DAW control, which usually means some time on your part setting up the controller and becoming used to your own unique workflow.
In my opinion you've only made a 'mistake' if you don't like the size of the keys. If that's the case, then you may want to swap controllers for one with full-size keys.
For that, you have a few choices:
1. Pick up a controller that you like (key size, physical size, and so on), and just plug it in and play without mapping any controls at all. In that case, you'll have to manually control your DAW with a keyboard and mouse, which isn't too bad, but does take your hands away from the controller.
2. Find a controller that is recommended for your favourite DAW and spend time mapping controls to your satisfaction. Personally, I use an MKII to control Arturia virtual synths regardless of the DAW, since they 'just work', plus use a Kontrol 49 for Native Instruments synths, since they also 'just work'. I find both controllers equally good/bad for DAW control (regardless of the DAW), with the exception of controlling Maschine with the Kontrol, which is seamless (obviously).
3. You can purchase a new or used hardware synth and enjoy turning it on and playing without messing around with anything. You can connect it via MIDI/USB and most new synths have USB audio out, which makes it easier to record and edit to a DAW. You can also use the keyboard a a controller, and many have great arpeggio features.
I'm not sure what your exact requirements were when you picked up the KeyStep - it's a great little controller, but if the key size is too small, then you can pick up an AKAI, which is roughly the same size, but has fewer full-size keys, plus pads. I purchased an AKAI controller at one point; wasn't overly impressed with the software or mapping, so I returned it. There are many smaller controllers in the price range of the KeyStep: Alesis V25, Nektar Impact, and so on, but they will all disappoint you in the sense that you'll have to spend time setting them up to work with your DAW.
Good luck!
