Experience/tips asking for work accommodations?

I work a regular office job in office 3 days a week and am thinking about asking for accommodations because the pain and fatigue are really affecting my quality of life. I’d love to have to more remote work time, flexibility with hours, etc. but not really sure what is reasonable to ask. Also of course very nervous about putting myself on HR’s radar. My rheumatologist said she would write me a letter but looking for any insight folks have of what accommodations they asked for, how they phrased the symptoms/impact on work/etc.