Stretches/Exercises to fix these issues?

Hi everyone!

Im pretty unknowledgeable on all things stretching and training and such, and wanted to ask if anyone of good ways to improve a few issues of mine?

1. My posture is really bad. Anytime I try and sit up decently straight, after a minute or so I’m really sore and can’t really hold it anymore. Maybe weak back and core muscles?

2. I’m unable to sit on the floor in any position without having both hands on the floor holding me up. In addition to that, I can’t sit cross cross on the floor, as my knees can’t really go down at all. I think this is tight hips as well?

I’m really wanting to be able to do those things listed above, and wanted to make a routine of exercises and stretches, but really wasn’t sure what to do. So any advice would be greatly appreciated! Thank you!