I've also been out of school for many years, so I feel your pain on this one. My advice would be to first, try to get over you hesitance around asking your recommendation writers to look over your SOP. If they've already agreed to help you with a letter, it's very likely they would be willing to give you some notes on your SOP. It doesn't hurt to ask, although I know it can be intimidating. Also, if you don't have connections in your field, it wouldn't hurt to start making some now. Try reaching out to potential PhD advisors in the departments you are applying to. If you get lucky, one might get back to you and be willing to help you out if your research is a good fit for them. Be brave and good luck!