I agonized over picking the right size. Hopefully this helps you. I'm 5'6" tall, 155lbs, average athletic buid, 32 waist, 30 inseam. I bought a medium seen in my pics.The fit: all I wanted this for was winter walks with my dog around the neighborhood. I figured since I wouldn't be wearing the Booties or sleeping in it I'd go with a medium even though I was 1" taller than a medium is recommended for even when only using it actively. If I planned to sleep in it I definitely would gotten the large for extra room. As it is, the medium BARELY fits. I can walk around with no problem but the legs only reach my upper ankles, the crotch is pulled up a bit tight, and the shoulders feel like they're somewhat restrictive. Again, for 20 - 30 walks this is all ok. With the Booties on its definitely tight. Still wearable, but tight. When I raise my arms up the sleeves get pulled way down to my forearms and the crotch pulls up even tighter than it normally is. I didn't get a large because I didn't want this to be baggy at all when I was walking around. I wanted to be able to put a layer over it when it got below freezing and still walk outside comfortable. The medium works well for that and is just comfortable enough to not be annoying.As far as the selkbag itself goes, it's super comfortable and super warm. Honestly it's as warm as any of the down winter jackets I own with the added benefit of keeping my legs just as warm and not letting drafts in as even the warmest 2 piece winter outfit would. The zippers all work well and are easy to grasp even with light gloves on. The elastic hand pouches at the end of the sleeves is great for keeping the hand warm while still allowing you to slip your hands outside of them if / when necessary. The kangaroo pocket is convenient although the material on the external portion of the pocket is not insulated like the under layer is. The hood is just as warm as the rest of the bag and clinches up nice with the Drawcord. The material of the back really is buttery soft all around.At first I thought of getting the original model but I'm glad I didn't as the lite model is plenty warm enough without all the extra baggy ess that would impede mobility. I suppose if you're winter camping, or depending hours outside in sub 40 degree weather you might want the original, but for an hour or less outside, even down to 36 degrees this is enough.