Not telling you to suck eggs as I can understand why you would want just one layer for ease, but the best way is to actually layer clothing. The Kiwi's and Poms seem to have it sorted with layering.
I have a Frosty Boy and find it too hot, unless it is really cold (Under 6 Degrees).
My commute is 25Km's and I go through some very cold areas. I layer up with a no longer available Lab Gear under shirt, a super Roubaix winter jersey and a
ROUTE 7 Hi Vis Windproof Vest.
For the bottom half, I found a normal set of Bib shorts with a set of
Prorace Windtex Coated Winter Bib Tights Without Padded Insert over the top, with a set of GE Lucifers for socks (That reminds me, I need to buy a couple more pairs)
Under the helmet I wear a
Prorace Winter Under Helmet Winter Skull Cap.
A set of winter gloves as well.
Benefit of layering is you can take it off in stages as you warm up. To get it all home, I also wear a very old Camelbak Narrow Gauge (Hands up if you know what one of these look like
). I think the HAWG replaced it about 10 years ago. This Camelbak, no longer has a bladder and because of its thin profile is great for commuting on the bike. In the Camelbak, I pack my Fox Incline gloves (I use these on my roadie as I hate fingerless gloves), a standard jersey and socks. So if it is warmer in the afternoon when I leave, I can swap out gear, until I am happy that I am warm/cool enough.
I think I may take a look at the Baked Alaska, to fit in the gap between over kill of the frosty boy and the GE windproof Polartec vest, which they no longer make.
The layering system