I used a stretch shirting from Gorgeous Fabrics, so it's extra comfy. I did a quick muslin to check fit, and ended up cutting a M, then taking it in a bit around the waist and hips since he likes a slim cut. The fit isn't perfect (and neither is the construction), but it's pretty good for a first effort.
I made a few improvements over the original pattern inspired by Lisa at Notes From a Mad Housewife: I changed the sleeves to be one piece instead of two, and added a sleeve placket. I drafted a straight yoke and used the burrito method to attach it. I also flat-felled the seams, which is certainly against my naturally lazy nature. Must be true love if I'm willing to flat-fell seams!
The only problem with this shirt? Now he wants more...
Pattern: McCall's 6044
Fabric: Stretch shirting from Gorgeous Fabrics
Modifications: Added sleeve placket, straight yoke with burrito method, one-piece sleeve.