Several of our group are big fans of KR stuff.
But their website is hard work.
The M2 and M4 trays trays are a decent fit - it depends if you want to stand up figures, or lie them down, as to which depth is best.
For bigger stuff its pretty easy to customise a few slots in a tray - as most WM monsters are generally only big in 2 dimensions. You can always cut out a few slots in a higher tray to fit in a big figure like a stegadon.
Personally I magnetise all my WM stuff, and use box files lined with steel paper.