amazon.com appears to still have have the long fermometer strips @flars mentioned. If you have a local homebrew store, they may have them as well.
One gallon carboy geometry suggests that you could put the carboy in about 4" of water with the new FermagraF°™.
- it's 8" from the bottom of a one gallon carboy to the bottom of the "one gallon" lettering
- the taper of the carboy starts at about 7" from the bottom of the carboy
- FermagraF°™ are 3" x 3"
- so that would leave about 4" of water for the carboy to set in.
4" of water may be enough.
Also, I have trimmed the long fermometer strips to fit within the ribs of the Little Big Mouth Bubbler®:
so it may be that the FermagraF°™ can be cut in half to add 1.5" to the water that the carboy can sit in. Packing tape on the bottom of the fermometer or FermagraF°™ does offer some resilience to water splashed on it.