This my approach too. I tried heavier jackets but found them too heavy or too tight or both. I am a big fan of multiple layers of merino wool (smartwool, etc). I have them ranging from fairly form fitting to pretty loose so that i can layer one over the other. Two layers and a shell is good down into low 30s. 3 layers has been good down to 15. Now if I can figure out how to keep my feet warm.
+1. Wool rocks, amazing material-keeps you dry even when your wet, cool when hot, warm when cold and it never stinks. Amazing. Only thing I buy now.