Well, what I did (I have two of the model 142 FNs) is change out the floor and add barriers. The cage pan that comes with the cage is slightly smaller than the inside of the cage and hedgehogs can get their feet caught. I managed to get away with using the pan for about 1 year before Cuda managed to get his foot caught. Luckily, he was without injury. I went out the next day and bought a piece of coroplast to fit in the floor and we haven't had issues since.
For the barriers on the main level, I just cut coroplast to fit and few/tape it on. Put the coroplast on the inside to discourage any climbing and your cage is instantly baby safe.
If you're going to keep the second level in, put it at the lowest possible setting so the ramp is at the lowest degree of incline possible. Fully enclose the ramp and the level, and you should be good to go. The ramp can be fully enclosed by arching hardware cloth over it, using a plastic tube or adding walls that the hedgehog can't climb.
*Lisa* on here has great photos of how she modified her FN.