I think I want to buy a Hot Sling in Fleece for my newborn. According to the sizing calculator, I would need a size 3. Can someone tell me if the size chart is accurate.

I think I should size up to a 4 to be safe since the size 3 says it is for people that wear a size "s-m" shirt. I am for sure a "m" shirt and never a small. In some brands I buy "L" shirts which is why I tend to think I should buy the size 4 since it says it is for people that wear a size "m-L" shirt.

I wanted some feedback from others that own this pouch before I decide what size to get.
Thanks!