I bought the large Superlight bivvy from MLD when I bought my Trailstar, I was torn between that and the bug bivvy but I think I made the right choice. The large version is made for taking thick mats like a Neoair or Exped. With my Neoair short, a PHD Minim 300 or Alpkit PD 400, I still have plenty of room to move about. I slip a TAR sit pad or my OMM Duomat under my feet.
I got one of Seans Oooktubs but only used it once so it's not really tested yet, it's mega light with the Chikara fabric and my useless Terra Nova tiny titanium pegs hold it in place nicely. I've picked up a few different inners but I think I prefer just a bivvy rather than a full nest.
I can see the benefit of a bivi, helping keep you on the Neoair and another layer of fabric. My large Alpkit bivi was just not big enough for me - felt like I was in a body bag.
Im liking the look of the oooknest tub, but do worry that I will be sliding off the thermarest all night. Ho hum, decision decisions & more virtual shopping