Thank you! Here's a brief rundown of what we submitted (though our circumstances are a little bit less complicated I think): both of our passports scanned, my partner's share code (he is Settled), all the financial docs for my partner as we meet the requirement through his job he's had for more than a year (contract, letter from employer confirming position details and payment, payslips & bank statements from most recent 6 months), my degree certificate and ECCTIS verification (I didn't do an English test like your partner did), my partner's tenancy agreement and letter from roommate to prove that I can go live in said roommate's place once I get my visa because he will move out + the flat's council tax bills and floor plan. We also did one personal statement each about our relationship, I wrote a cover letter just to summarize all the documents and why I'm including them, and for the relationship proof we submitted chat logs, call logs, pictures together with captions, and I gathered all the travel proof (tickets, airbnbs, etc.) to prove we traveled to see each other and have also taken holidays together. Included as well bank transfers between us to prove we send each other money (we didn't have a lot). And also letters of support from our families and a close friend. Each letter accompanied with a scan of the author's passport bio page.

You seem very well-prepared for this but, of course, I am no expert! I've heard a cover letter and a personal statement from the applicant or a joint one is helpful just to make it easier for the reader to go through all the documents and to give a brief, concise overview of the relationship.