What are some good excercises for a better posturee?

I have always had a good posture but due to some changes in life I use my body differently at many tines a day and I belive this will change my posture if I do not do regular excersice (my lower back feels tired nowdays)

What advices do you have?

Bad posture can be the result of muscles holding onto dysfunctional tension. The problem might not be that muscle X is too weak, but that your body (really your motor sensory system) has developed the idea that holding tension in muscle Y is normal.

There are exercises or “movements” geared for this. Try looking up “somatics.” It worked for me.