Best thing I ever bought for keeping warm was a Montane Featherlite Smock (although the price of these seems to have gone up) it doesn’t actually add any warmth, but it’s bloody effective at keeping the wind off, packs down to nothing. The cold riding for me is from wind, not actual cold a lot of the time, so a windproof makes a lot of sense as a starting point.
Other than that, I just use baselayers (smelly helly, Icebreaker etc.) underneath a windproof. The only time I really feel the need for proper cold weather gear outdoors is winter climbing, and even then I walk in a baselayer and windproof, and then climb in a pertex and pile smock – that’s done me proud down to -20°C or so if I’m moving and belaying, with a down jacket in the sack for emergencies.
I tend to run hot and not feel the cold as much as many people, so YMMV.