I'm hoping to order my very first TeeFury shirt today (cause Stargate!), but I'm stuck on sizes. I measured every shirt in my closet, but it's not helping. The smalls I have are smaller than the small on the sizing chart, but my mediums are smaller as well. Unfortunately, buying two isn't an option (boo money) so I have to just get one and hope for the best. Are the smalls usually pretty small?