The superlative of "often" is "most often."
"Most" is the superlative of many.
most often
most often is the superlative degree for often
What is the comparative and superlative of Often
OFTEN
more often, most often
Most often
more often, most often
more often, most often
more often, most often
more often, most often
more often, most often
Comparative: More oftenSuperlative: Most oftenmore often, most oftenmore often, most often
Sleep is a noun and does not have a superlative. Sleepy is an adjective and the superlative is "sleepiest."