Hi Cat! I used to play violin
My suggestion would be to call your osteopath and see what they recommend for ways you CAN exercise and stay more active without stressing your back. As far as diet, any plan that increases vegetables while getting enough protein and at least SOME fats is good. But the more veggies the better. See about a calorie tracker app, but fruits and veggies are a good way to feel full (all that water and fiber) while minimizing calories in.
For the time being, while you let your back rest and heal, you may want to focus on maintaining and not gaining and leave the last few pounds until your back is better. What I have found, being a swing dancer and knowing many other swing dancers who don't rest like they should with various injuries, is if you don't really give the injury time to rest it will be a problem for MUCH longer, if not permanently. It looks like you are a healthy weight so as long as you focus on eating healthy, staying active in ways that won't bother your back, and resting your back, that is more important right now and in the long term than losing those last 5-6 pounds. If you don't take care of your back now, you may never be able to adequately be active enough to drop the last few pounds.
So eat healthy, REST your back, maintain at your current weight, and worry about the last few pounds AFTER your back is better.
~Katy