I called and was talking to them at the Alaskan shop the other day and the lady suggest that I put the froli system under the mattress. She said that it would fit with no issues.
Just keep in mind that there are actually THREE Froli systems, the Traveler, The Star, and the Zona. The Traveler is 1 3/8 inches high, the Star is 1 3/4 inches high, and the Zona is 2 3/8 inches high. You're probably safest sticking to the Traveler.