Your surgeon should have notified PRP of your disability. It would be a good idea to ring yourself and check that they are aware.
Having the dye injected is done on the same bench as an ultrasound, it is reasonably wide.
it is not the nicest thing to have done but bearable. Massage that breast well, it helps to spread the dye. My nurse offered to do it for me if I didn't think I could, so say so if you don't think you can.
The CT machine bench is similar but narrower and they do have securing straps if you need them. The hardest thing there is lying so still for so long with your arms up.
If you have worries, voice them.
I found the nurses very compassionate and helpful.