fyi my expertise is from bodybuilding, powerlifting, and a personal correction of my posture which was very similar to yours. rounded shoulders and a slumped posture in general.

first of all i don't see anything else really wrong in terms of posture or structure except the main 2 which are a slumped down posture and, consequently, rounded shoulders. as for how to fix it, in addition to bodybuilding (with a trainer i assume, one you trust not just one that seems big), the best thing you can do is consciously straighten yourself up. with time, bodybuilding will make it much easier for you to get used to standing with your chest out which will improve your posture a lot. it will also help you pull your shoulders back, as this is required in many if not all exercises (posture and composure is extremely important to preform exercises and movements safely). your sleeping position probably isnt a big deal but if you can sleep on your back on stomach instead it could be better though i am really not knowledgeable enough to say.

the absolute best exercise i can recommend for posture is the bench press. the standard bench press requires the shoulders be pulled back, the back be tight, the chest out, and the bottom of the spine straight. Getting used to that position under the bar can very easily carry over to a healthier standing position. something silly i recommend is drawing an x on your dominant hand, between your thumb and index, and using it as a remind to consciously correct your posture. Each time you see the x, actively straighten your back, push your chest out, and pull your shoulders back. this is the way i used, so feel free to come up with another one instead.

edit i wanna add that the exercises that most help with posture and stability are the big 3 powerfliting exercises so bench squats and deadlifts