I'm 5'6 and am looking at purchasing an inflatable air pad to put in a bivy. I want to get the therma rest Neo air because they are rated best, but Idon't know what size to get? The small is my exact height but the regular is around a half foot longer. Should I get the small and save just a few grams? But will I regret not having the extra length later? What are the pros and cons?