I would try a different hold for your left side. Also, that's great you have a good solid eater, but I can understand your concern. I would continue to offer breast and try not to offer solid instead of breast. You could be on a slippery slope if you continue. Maybe try some expressed milk in a sippy cup instead of solids.
Of course, I'm not sure what your routine looks like. Maybe your lo is ready to have solids twice a day already.