i want to visit China for tourism

Abena, your husband also needs a tourist L type for China if he holds ordinary British passport.
As for the invitation letter, you are advised to find an agency to help you get that. The agency can always find a way to solve this kind of problem. Or you can book a tour from a travel agency, and then the travel agency may be able to get the invitation for you.
The application process is as follows:
First, prepare the relevant documents including passport and its photocopy, a filled-out application form, a recently-taken passport-style photo, introduction letter, an invitation letter, round trip air tickets, hotel reservation, and recent 4-month bank statement.
Next, go to China embassy to submit the application.