I think discouraging frequent long rests would be a good way. Keep in mind that the number of spell slots and other ressources you get in dnd is designed to have 4-6 encounters before you long rest.
Given the story and our condition, it would fit quite well to add some permanent debuffs when long resting too often. (Honestly I was actually quite disappointed on my first playtrough that there weren't any bad consequences for ideling around instead of looking for a cure.)
They could say, if we take too long, the Emperor has to sacrifice some of our own power to hold up the defences. Maybe permanent -1 to Con, Int and Wis (or all stats) for every 7th(?) long rest we take? So every time we would transform if it was a normal tadpole, we loose a part of ourself.
