all the right grasses that don't take over the wild flowers Any grass will crowd out wildflowers if the nutrient levels are high. While some of our traditional wild flower meadows have been lost because they're been dug over and reseeded with fast growing grass, mainly they've been lost through addition of fertiliser. The key really is to get the nutrient level low when before you start.
Also be clear what you're going for - "cathyandclare's* meadow looks to be lowland, relatively damp grass, and is full of red campion, stitchwort, fox and cubs, foxgloves and giant bellflower on the woodland edge, daisies on the mown path -it's absolutely beautiful, but that's a very different mix than on a traditional Yorkshire haymeadow. And different again from the cornfield mix of cornflowers and poppies so often planted by Parks Departments (and don't get me started on "wildflower" meadows full of Phacelia and Cosmos).
I must admit, if I had my time again I'd buy lots of plug plants and bulbs, and plant them in the existing lawn, lots of crocuses, daffs, daisies and cowslips etc That approach works well with bulbs but plug plants are every bit as difficult as seed to get established, and more expensive. I've done two meadows that way and neither are entirely satisfactory. If I had my time again, I'd strip the turf completely and discard, taking the fertile top few inches of soil with it, and start again from seed.