Hi Brie12,
I hope that what you spotted wasn’t a bed bug :sick:
I don’t have any personal experience with bed bugs or mattress encasements to protect against them (I’ve never used one or had an infestation) but perhaps some of the members here may see your post and share their own personal experiences.
Post #2 here has more information about mattress encasements that would protect your mattress from bedbugs and some of the thin membrane type of mattress protectors listed in post #89 here also make full encasements that are bed bug proof.
Phoenix