Poor coordination, knowing how to hold your body parts

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Can anyone suggest a good resource for knowing if I am holding my body properly?

I have poor coordination and body sense. When I think I am straight I am often crooked. I have no mirror other than behind my bath tub. I have been in physical therapy recently and we worked a lot on core strength so reminders of which muscles to activate helps, but I can't seem to apply it at home on my own,