I have as pet companions, 3 80#++ senior rescued Collies. All 3 are displaying joint & muscle discomfort.    I ordered the (chocolate) 37 x 56 as my dogs stretch out to rest. Two of the 3 dogs seem to enjoy the comfort, softness of the fabric cover & mattress/pillow fill. They like resting their heads on the bolster pillow ends & their backs on the support bolster back. This size is wide enough & the length of the bed, incl. the bolsters is perfect. Zipper is sturdy & well hiddened.

Pros: Having an additional reversible, washable quilted pillow seems to provide additional support & yet the bed remains firm & in place. I would definitely recommend this bed! 
Cons: It takes 2 people to properly insert the 3 bolsters into the bed cover. Also, even though there was an instruction sheet, it was perplexing tring to figure out the logistics of the bed cover.