Well, yeah, you could do vertical landing or water landing. Both have precedent, but water landing probably implies craning the drones on board, which is slow. Vertical landing on the other hand might work well. You'd still need a flight deck for that, but a much smaller one.
I guess something helicopter-carrier sized? I would think the main thing would be to avoid supercarrier sorts of ships. Smaller ships with similar capabilities would mean you'd be able to field more groups.
