Double element thermostats are common in hot water heaters which have
two heating elements.
In a bator you only need a single element but it should be the most precise
one you can find. You want one with a narrow differential, which is the range
it turns on and off.
For example, most Lowe/Home Depot type tstats may turn on at 95 then off at 105.
You want one that turns on at 98 and off at 101. The temps I list are examples
and may need to be changed for your bator.
I hope this makes sense from a half asleep electrical geek.