Okay, let's see what you have.
I'll arrange it into the correct upload sections for the application. Missing documents are in red.
Application DocumentsFull scan of applicant's passport - every page
Applicant previous passport - every page (or maybe this goes in the Other section - not sure)
Sponsor declaration and consent to checks form (part of online application)Proof of Identity/Travel HistorySponsor's passport - every page
Applicant's BRP
Residence in the UKAccommodationTenancy Agreement (joint name)
Latest Council Tax billCohabitationMarch 2018: council tax bill, joint names
August 2018: bank letter, DH, bank statement, me
January 2019: bank statements, separate
June 2019: water bill, joint names
November 2019: water bill, joint names
April 2020: bank statement, DH, tv license, me
September 2020: ?FinancesPayslips Feb - August 2020
Bank Statements corresponding to each payslip
Employer letter
P60
Employment contract
OtherMarriage Certificate
Also, am I correct in recalling that since I have an original tenancy agreement in our joint names that I don’t need anything extra from my letting agents?
Yes, nothing more is needed from the letting agent, but you do need your latest council tax bill to show housing costs