Hi Beemer,
How are you getting on with your Scandalli AIR III? I hope you are enjoying it!
I have spent a lot of time recently studying the Scandalli AIR series of accordions and I am shortlisting the Scandalli AIR III and AIR IV models as potential future instruments for myself (I can dream

).
For anyone not familiar with the AIR III, it's a compact accordion (19mm keys) with a weight around 9.9kg, though it could be lighter or heavier (I have seen other weight figures stated online etc). Either way, thankfully it's not a very large and heavy accordion like some of the 14kg to 16kg+ bayans out there.
For reference this is the model:
If the weight of the instruments is all on one leg, maybe you could look again at how your shoulder straps and back strap are adjusted. Perhaps the weight could be distributed a little more evenly that way, whilst giving a good playing position. I don't really tend to have the accordion sitting on my left leg when I play. I keep my left leg tucked out of the way. The accordion is above the leg rather than planted firmly on it. I let the shoulder straps and tightly adjusted backstrap take the bulk of the weight.
However, I don't want to cause you any further difficulties, so maybe as another idea, a little blanket could be positioned under the point of contact on your leg to help reduce the discomfort? I have a lot of natural padding

- which helps.
Finally, have you considered your seating? I always found a drummer's throne to be the best for obtaining a comfortable seating position, certainly better than a restrictive piano stool, in my opinion.
The only other thing is maybe take the accordion off before you stand up. The last thing we want is for you to fall and put a dent in yourself.
Good luck.