Hi, my name is haymaker63! due to have a full knee replacement. only gets ssp can we claim others?

You can use a benefits calculator to check entitlement to Universal Credit. As it's a means tested benefit then you will need to claim as a couple and your joint circumstances will be taken into consideration.https://www.entitledto.co.uk/benefits-calculator If you have savings/capital of more than £16,000 you're excluded from claiming. 

Are you claiming any other benefits?

Unless you live in Scotland he can look at claiming PIP. It's a disability benefit which isn't means tested. Whether there's any entitlement will depend on how is conditions affect him. More information here. https://www.citizensadvice.org.uk/Global/Migrated_Documents/adviceguide/pip-9-table-of-activities-descriptors-and-points.pdf 

https://www.ageuk.org.uk/information-advice/money-legal/benefits-entitlements/personal-independence-payment/

If in Scotland then it would be ADP. 

3 months before his SSP is due to end, if he's still unable to work then he can claim New style ESA, providing he has the correct NI contributions in tax years 2021/22 and 2022/23. Payments won't starts until the SSP ends because it can't be paid at the same time. He will need his SSP1 form and a fit note to claim it. https://www.gov.uk/guidance/new-style-employment-and-support-allowance#eligibility If he claims this as well as Universal Credit then the ESA will be deducted in full.