You're right, and Inspiratory Muscle Training is an easier alternative to playing didgeridoo, and it's very important to mention Mandibular Advancement Devices and soft cervical collars(since neck-jaw position matters, this is a big part of why apnea is worse on your back), but the thing is- it's unlikely to be enough.

Ultimately, to REALLY fix Sleep Disordered Breathing, usually you want maxillomandibular advancement - to move your jaws forward, which physically enlarges your pharyngeal airway which is where the actual collapse happens. Collapse that shouldn't be able to reach the point of increased airway resistance with a skeletally sound airway.

Many people also have nasal breathing issues, and while this can be caused by a deviated septum or severe turbinate hypertrophy,usually nasal throughout correlates with the cross-section of the nasal cavity, which is most effectively addressed by bone-borne(not tooth-based!) palatal expansion.