When I lived closer to work I used to run every day both ways, 12km in total, so 60 km per week. (Nowadays I run with my child in a jogging stroller, so I don't

When I lived closer to work I used to run every day both ways, 12km in total, so 60 km per week. (Nowadays I run with my child in a jogging stroller, so I don't need a backpack, and it's a hilly 8km one way so I don't do it every day.) Now I always wore a backpack with a chest strap like you said, and I never had a harder time breathing than normally. It wasn't a giant pain. And I didn't have problems with getting the things inside the backpack sweaty. For reference, this is a 13 liter standard cheap daytrip backpack. If you want to get fancy, Salomon do a vest-like backpack that has a good rep in ultrarunner crowd, with literally no bounce whatsoever. My experience with headlamps is more limited, but have you tried the type with the battery pack not on your head? The key to reducing bounce is reducing sprung weight.