It is very important that you keep moving, even when been given the diagnosis of Tietze.
Some useful advise regarding mobility
Stay within your boundaries. Don't exert when moving. When the disorder is dormant and there is little pain, you can do more than when the disorder is very active. A physio therapist who is acquainted with Rheumatoid diseases can advise on suitable exercises. There are many options: individual, group therapy, swimming, medical fitness and adjusted forms of sport.
Advise about sport depends very much from you own personal situation. Contact sports and sports where the body is exerted and locally stressed can better be avoided. More suitable are fitness, swimming, cycling and walking. With swimming, cycling and walking, your movements are regular and there are no shocks that put stress on the joints. Swimming and exercise in warm water is a very good way of moving. In water the joints are hardly exerted and it even supports the joints. When cycling you can protect jour joints by choosing a lower gear and by sitting straight up. A reverse brake can be more comfortable than hand brakes. Obvious there are more sports and exercises that can improve your condition. Important is that it suits you and gives you pleasure. You physiotherapist or GP can give you advise.
You can also exercise within a group. Many Rheumatism Patient groups organise besides so called dry exercises sessions also hydrotherapy sessions where under the supervision of a physiotherapist you can exercise in warm water. Often water exercises are combined with exercises outside the water. It is proven that members of a group therapy can raise the discipline of exercise.