A 56-year-old man comes to the clinic for a follow-up visit. He is being evaluated for obstructive sleep apnea following complaints of loud snoring and excessive daytime sleepiness. He filled out an Epworth sleepiness questionnaire and scored 10. He has marked anxiety whenever he is in confined spaces. He does not smoke cigarettes or drink alcohol. His temperature is 37.0^oC (98.6^oF), pulse is 80/min, respirations are 18/min, and blood pressure is 136/82 mm Hg. Pulse oximetry on room air is 99%. His BMI is 32.4 kg/m². Polysomnography shows an apnea/hypopnea index of 4 lying on his sides. This increases to 12 when lying supine. No arrhythmias are recorded on his electrocardiogram.

Which of the following is the most appropriate next step in his management?