Hi Mellisa,
I can relate.
My first garden was in yellow clay. My current garden is in 'Carolina Gumbo' a type of black clay.
In both cases the soil was actually nutrient dense, the plant roots just couldn't get to them. My gardens got better each year as I worked the soil.
You are on the right track...keep digging in organic matter. Shredded leaves, grass clippings, straw all work well. Best time to till or dig it in is late Fall/Early Winter so it has time to decompose before you plant again in the spring.
I also bury kitchen scraps into the soil in the winter (instead of the compost pile) and also bury a bunch of fish heads.
The best way to break up clay soil?? COARSE sand. NOT fine sand....it makes cement.
But a good coarse sand dug in real well prevents the clay soil from 'clumping' together.
Mulching is great too...because you can till it under in the early Winter. Just make sure you don't apply it until you soil is very heated up for the summer...if you jump the gun the clay will stay 'cool' under the mulch, causing very late crops.
Back to those worms. Red wrigglers work fine...you may want to save your money.
To 'box in the bet' I've also added worm eggs that I purchased. Nightcrawlers also are quick to digest the organic matter and leave their fertile castings behind.
Here's that black clay gumbo soil in my garden a few weeks ago...
Fiery REgards, Pepper Joe