I've also used buffs but ended up cutting them in half because they're way too long. The winter collar things are great as they're a bit baggy at the bottom so cover the top of your chest if you open your jacket a bit. Not sure if they do them anymore but they'll be on eBay/archive https://www.rapha.cc/gb/en/shop/winter-collar/product/WCL03XX
I've also used buffs but ended up cutting them in half because they're way too long. The winter collar things are great as they're a bit baggy at the bottom so cover the top of your chest if you open your jacket a bit. Not sure if they do them anymore but they'll be on eBay/archive https://www.rapha.cc/gb/en/shop/winter-collar/product/WCL03XX