Can I use Comfey's "Flower Selecting" Ability or Colress's Experiment if I have only 1 card left in my deck?
You can play either of them with only one card left in your deck; but you have to put the card into your hand, you cannot discard it or put it into the Lost Zone.
Source: TPCi Rules Team (2022-10-06)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH11_79
SWSH11_79
SWSH11_155
SWSH11_155