Annual/Wildflower mix

I have a steep sloped semi-shaded area at the side of my house which I feel would lend itself to a small wildflower meadow. With this in mind I spread three packets of wildflower seeds in the spring, topped up with my own self saved poppy seeds and sunflower seeds onto recently cultivated bare ground.. I also planted an odd chrysamth and dahlia on the site.
In the summer I had a lot of foliage and a few flowers,but not anywhere near the selection I had hoped for.

I now have reasonably bare ground again once I pull out the odd weed. I know you can sow annuals in the autumn so wondered whether anyone could point me in the way of a good seed mix that they themselves have had success with?

I don't want to spend a lot of money on the bed without some guarantee of success so would probably go with three packets of seed again?