I am in a kind of similar situation as you are. I recently also had to travel quite a bit for work and worried like hell about my just all bought modular stuff. I was thinking about an Intellijel 7U case (with the option to extend with yet another same case that can be connected with some metal connection plates, optional available/purchasable). But just at the moment I actually almost bought the Intellijel 7U case, for my situation I decided against it...
I bought instead an Elektron A4 (Analogue Four), it's nice small and handy and fits in my hand luggage. So I don't have to worry which modules I put into a casing that most likely is going to be too small soon enough anyway. So opted for the A4 when I am abroad and I play with my modular whenever I am at home. Might be not what you wanted to hear but I had too much "headache" regarding deciding which case would be good and big enough but is still comfortable to travel with, etcetera. I admit it might not be everybody's choice of "solving this", but for me this worked out great.
Your Digitakt, if I remember well, is even a bit smaller than the A4, so there should be even more space left in your suitcase!
Good luck with the projects abroad and kind regards, Garfield Modular.