You definitely need fast access as you will be stalked. Did you see that 103 year old granny with a walker get mugged the other day? Bad Guy punched her in the face a few times, robbed her then punched her again.
(Like Clint Smith says, "Some people just need to be shot!
).
So, being handicapped you are an easy target...unless you're armed!
I am glad you are aware of your surroundings, too. That's 90% of it...
I think the gun should be "Open Carried" for fast access. It will be a deterrent in my opinion, especially since most muggers are cowards praying on the weak and elderly. They may be afraid of the gun. But the flip side of that is they may try to take it. So, I think the Serpa Holster from Blackhawk would be a good choice, it has a trigger lock for weapons retention security. And the Bad Guy may not know how to push the button to release the gun, and from his approach angle, it may be hard for him to get to the button with his trigger finger.
Further, the gun is VERY secure and won't fall out, especially when you put the wheel chair in and out of vehicles.
Between the legs would be a good spot, too. For both convenience and weapons retention.
Hope this helps.
Take care,
D.R.
www.TacticalShooting.com