Kammock’s firebelly down quilt is amazeballs with the mantis. its not cheap, but its a made-to-fit fit and its awesome. Packs down to the size of a nalgene bottle

Pair that with one of those costco down throws and youll be a snug bug

DBD Packable Down Throw (LAPIS) https://www.amazon.com/dp/B074PJ7C4C/ref=cm_sw_r_cp_api_i_URD2Db8PH2K36