Broken Balance Springs

Trying to find replacement springs, or the complete balance system for both sides of my bathroom window. Double hung vinyl coated tilt-in type, thermo-pane. Weight 12-13 pounds.

Attached photos of current balances. Coil spring has number 9 embossed on it just above attachment screw. The top white plastic piece that holds the coil has a "B" embossed on front. Original balances were replaced by a contractor 5-6 years ago. My parts are probably not OEM. But window worked fine until springs broke again.

The two main plastic pieces are 1 1/4 in. wide. Spring is 1/2 wide. Plastic bushing that holds spring coil is 3/4 in. OD. Thanks for any help.

Thanks for quick response. Have two questions. First, as I said in my original post these pieces are replacements and the contractor said they were not exact matches, just what he had with him. Wouldn't the 9 lb. spring I had, and the 9 lb. you recommend be too strong for my 13 lb. window?

Second, after I pushed the plastic bushing out of the broken spring I could not get it to go back into the spring. Would I have the same problem with a new spring? Does this take a special tool or something. Thanks, Ed.