Replacements for coil window balances

Hello! I have a 23 year old house with a window that has a coil balance on either side. Both of the springs have broken, leaving a short section up by the support. The window is obviously now very heavy and won't stay up, and has become a safety concern because it is the bedroom window of our special needs son.

Attached are photos of the shoe installed and removed. I do not see any stamp on the spring, nor anything on the shoe that indicates what replacement spring I would need. The window sash weighs 19.6 lbs.

I would be open to ordering either two replacement coil springs, or replacement support/shoe as well... though I'd prefer to just replace the coil springs since I know the existing support/shoe will work. What would you recommend?

Thank you!

- Jeff

one more photo