Tokyo? Never really very cold there - they get snow, but not very often and then not very much. Unless you have bad circulation, are from a tropical climate or are just plain weak you窶冤l hardly ever feel cold outdoors. A moderate weight fleece top for the winter months - but you'll feel hot on the subway.
I can talk about apartments but I assume you're going to be staying in a hotel - in which case you won't be cold indoors.
If you need to be wearing suits when here then insulate from the inside out - most middle-aged Japanese men wear long-johns all winter - as do most JET teachers posted to cold regions.
