As someone has suggested - Tai Chi/Yoga/Pilates will help to tone and stretch muscles and improve core strength - you can get dvd’s to follow that are specially for people with mobility problems. Working with a ‘gym ball’ is also good - in fact you can use one of these to sit on whilst watching tv/working on a pc. lt encourages the stomach/back/thigh muscles to work.
When outdoors - playing with your son - try walking poles. They hold you up well - and do not look like walking sticks or crutches.
l can understand you not wanting to come out with the fact you have MS - at work. Because, hopefully, you will get over this set back and recover from some of your symptoms. But you do have to inform the DVLA if you drive - and your car insurance/holiday insurance/health insurance -
One thing about any exercise - it does give you a ‘feel good factor’ - so good for mind and body.
l have an eliptical trainer and a powergym vibrating machine. 10mins on each everyday has kept me reasonably fit.