Pufferfish definitely don't work with lionfish since they will eat the lionfish's fins. In my 40B I have several of the dwarf lionfish species and a small snowflake eel. I know the eel will eventually outgrow my tank, but he's small now and he's grown over the last 8 months, but not that much. Any of the dwarf lionfish species (fuzzy, zebra, Fu Manchu) would do great in your 55 gallon. The medium bodied, like an antennata would be fine as well.
My lionfish are never aggressive, so as long as I pay attention to where they are while I'm working in the tank, there's no risk of being stung. I also wear very thick, over the elbow gloves when I'm doing a lot of work in the tank, like messing with the scape, placing corals, or fragging. That way I can't accidentally bump into a lionfish spine while I'm working. Honestly, if you're careful and pay attention, you are very unlikely to get stung.