Since i began mewing in early 2017 i have struggled with maintaining correct oral posture whilst sleeping for 2 reasons and was wondering if anyone could have any input to help me and anyone else struggling with a similar problem.

Firstly, i struggle maintaining a lip seal. This is because i suffer from a mild amount of mentalis muscle (chin muscle) strain when i close my lips. This means that when i fall asleep, my lip seal is broken which encourages me to breath through my mouth. How can i improve this resting lip position?

Secondly, i find that when i lie down on my side or back, breathing through my nose becomes noticeably more difficult. Perhaps this is due to soft tissue in the nasal cavity changing position when lying down and impeding the flow of air through the nose? How could i fix this issue too? I was thinking perhaps upper jaw expansion may create more room in the nasal passage so this issue can be avoided. However, I'am currently wearing a retainer from previous orthodontic work, which is likely to prevent any kind of upper jaw expansion for now.

Any input would be greatly appreciated, thanks!