Every baby needs a green jacket and hat. Especially one from his Grammie.
Pattern, also by me. A basic little jacket worked bottom up, with sleeves picked-up and worked down. Hat is also a basic hat. Don't ask for instructions; there's aren't any. I just did my thing.
There's garter stitch at the top of the jacket, because I love to work it, and it shows off the variegated yarn differently than stockinette. Garter cuffs on sleeves, also. No sleeve shaping at all; I want the sleeve to be wide enough for his little arm in a onesie to get through easily. Bottom of jacket and hat have 2x2 ribbing just to hold in a little, especially on the head.
Either it will fit, or it won't. I don't worry much about this stuff. The process is what's important here. I like knitting little garments, and if he can wear it, good. If it's too small, then his Mom can donate it to the annual NAMI auction. If it's too big, he'll wear it eventually.