Below are a few mailshots that I have research to give me a basic idea of what a mailshot should look like and how designs can be applied to an envelope such as adding designs inside the envelope like a mountain or in my case a bike.
The envelope below shows different ways of creating envelopes, it would be suited to me because my design will be printed on the inside as opposed to information cards.
This is just a mix of envelope designs I could take inspiration from. Particularly the different styles of envelopes.