first night out in the hmmk- i used my orange Z-rest - got chilled at the 40* mark, but was able to get decent rest, i.e. was not fa'fa'freeeeezing
please note--this was my 1ST NIGHT -- YMMV
i've seen a buddy use the wide sized neo air between the layers, and it looked very comfy!
i've also had luck with the stuff wbguy recommends,,, landau foam.
wide pieces, various thickness, easy to customize to your needs.