You can buy ready-made wildflower meadow mixes for different soil types and situations, and it’s worth looking for a mix of annual and perennial to prolong flowering time. Seed mixes are also available in different colour combinations.
Or you can buy the seeds separately and mix them yourself.
Seed mixes vary, so check the coverage on the packet. However, as a rough guide, you need 1g per square metre of pure wildflower seeds and 5g per square metre of grass and wildflower meadow seeds.