Looking for an image editor

I'm looking for a decent program to use to edit images. The problem is that I have a few specific requirements, and so far the only thing I know of that meets them is an old version of Paint Shop Pro, from back before Corel bought and ruined it.

I can (and do) still keep using that, but it is pretty outdated and has some weird quirks, like being able to save PNG files with transparency but not load them (transparent areas get converted to an arbitrary colour), so I've been looking for something decent to replace it with. So far I haven't found anything that quite measures up.

So what am I looking for? This:

Click to embiggen.

What we have here is a single window with spots to dock toolbars on either side. I've got the tools palette on the left, the colour picker on the right and the tool options and layer palette floating, because they need more space.

It's not entirely essential that the toolbars be dockable, but it is pretty nice. The important thing is that I can open up several images within that one window and move them around over that grey background. I absolutely do not want to be able to see my desktop, it's too distracting, I don't want multiple copies of those toolbars, and I don't want images to open maximised to the full size of the program window.

I've tried Paint.net, Stylepix, GIMP, Krita and even Photoshop and none of them work for me. Is there something out there that works the way I want it to, or should I just stick with PSP?