You use the gear most suitable to the speed and road conditions - regardless of how many times you need to change gear. It ensures you are travelling safely and not putting unnecessary strain on the vehicle.

Also you don’t “have to change to 1st before I stop”. You can change to 1st after you stop. 1st gear is primarily used to pull away from a standing start, even at very slow speeds 2nd gear should suffice in most instances.

Additionally if you’re reading the traffic ahead of you suitably, you should be able to balance your momentum so that you’re not constantly have to stop/start in heavy traffic, you just roll along at a slower speed even if that means leaving a fairly sizable gape in front of you - unless you choose to weave though very heavy traffic. You can only go as far as the vehicle in front, so does it really matter if you’re 50 yards away as opposed to 5? You’ll usually find that you’ll end up catching up to the slow traffic without increasing your speed because they’re stationary more often.