I keep a heating pad at work. Mine's the microwaveable kind, because I prefer a moist heat, but I probably wouldn't use it if my seat at work was near anyone else's. The buckwheat filling smells a bit rank when heated up.

I also thankfully have a job that requires a mix of sitting and standing, so I try to mix those tasks up throughout the day to avoid doing too much of either at one time. Maybe see if your workspace can be made to accommodate an adjustable desk, so you can sit or stand as your body demands. Also, make sure you have a comfortable chair. These changes should fall under the reasonable accommodations that your employer is required to provide, if I understand correctly.

I go and do stretches in the restroom when necessary, as I feel awkward doing so in front of my coworkers.

Mary, 25, happily married pro photographer, momma to 2 great danes.
Dx: Psoriatic Arthritis, Fibromyalgia, Psoriasis, Sjogren's, IBS, Hiatal Hernia, & possible Endometriosis.
Meds: Stelara, Methotrexate, Relafen, Omeprazole, Lyrica, Tizanidine, Voltaren Gel, Tramadol