If free fixes haven't worked: an adjustable mouthpiece
The maker says SnoreRx Plus adjusts in 1 mm steps, and its FDA file describes advancement of up to 6 mm.
Not for: anyone under 18; signs of sleep apnea, or central sleep apnea: get tested first; loose teeth, gum disease, dentures or braces; jaw joint problems (tmj disorders); recent implants or major dental work.