Similar to the Proxis, you could go for the Samsonite C-Lite. They have an expandable and non-expandable version. Non-expandable is 20 cm depth and the expandable version can be expanded to 23 cm.
I have the expandable version and it does the job. Biggest drawback for me is the wheels. Compared to my Tumi it does not glide that well. Better drag it with you on two wheels when walking on soft ground like a carpet.