I sometimes go outside with my jumper on but feel t-shirt alone would be fine. However OP my problem is even bigger, because I have 2 options to consider:
1. I stay in my jumper risking overheating.
2. I take off jumper risking getting cold
Edit: I would like to thank Dwight Schrute for PMing me with solution to my problem. Your idea of unzipping my jumper solved my problem and I can smile again. You are great, thanks.