Rheumatoid Arthritis - Disclosing to work / reasonable adjustments

Hello all,

I currently work a fully remote role (contracted hybrid) but organizational structure has allowed all employees to WFH. **I did not have arthritis when I joined this role, it was developing but not diagnosed and I had no idea.**

I work a non-facing customer office role. Our organizational structure is changing and we are being mandated to 2x office days a week. I have absolutely no issue with this as I live 20 mins from the office.

My main concern is, I am always unwell due to my immune system being on DMARDs. I have had days where I'm able to WFH (don't have to talk to anyone, can have the heating on full, don't have to move around, get changed etc), but would have to call in sick if I was in the office. Also in the office it's a huge building and we cannot monitor air flow, so the office is always **freezing** cold due to air con which really hurts my joints. I'm so worried about getting unwell often too being surrounded by others as whenever I am in, I come home unwell.

I was going to ask, if I'm feeling unwell instead of being absent - am I able to WFH? Is this a reasonable adjustment? And if I'm in the office and I'm too cold and it's hurting - can I leave and WFH? Is this reasonable or not? I want to go in because I have so many friends at work, I'm not trying to avoid being in the office -- just want to avoid unnecessary days off when I'm ABLE to work / not working somewhere in pain.

My arthritis is in my fingers and hands, knees and legs. Thanks!