I'd second the suggestion for leg warmers if you'd like some flexibiity. I have a pair of Sugoi Subzero tights that are really warm (I wear them with PI Sugar Knickers so my knees are well covered). I love 'em. The other day, I wore a pair of Shebeest Wind Pros that were twice the price and much bulkier, but I don't think they were noticeably warmer. Sugoi makes several other tights, including the Midzero, that might be a good weight for you.

I would mention too that neither the Sugoi nor Shebeest tights that I have have a chamois. I'd just as soon have another layer on underneath so I wear either my shorts or knickers with them. Presumably I could peel them off if I ever got to warm mid-ride.