my mother was a great believer in good posture. it has turned out that she was right.
i am always more comfortable for longer periods of time when i can sit up straight while working on projects.
take a long, hard look at your work space. is everything at a comfortable height for you?
i have my own machine sitting on a raised surface.
whenever possible, i do my cutting on my ironing board or kitchen counter. (i bought a wooden cutting board, with a 12" x 18" mat to use on the ironing board.)
start with options that won't cost any money. if necessary, consider getting a shoulder brace that will help you train yourself to sit up as straight as possible. it will almost certainly make a huge difference. :-)