Oh Leanne, your poor thing. That must make life so difficult for you.

I don't have that problem but here are some things I can think of that might help:

Sling - the one I have, called a pocket sling, can be used even when they are over 1. You can wear him on your front, back or hip. At 12kgs it would still be heavy I imagine, but if you're carrying him anyway the sling would be much easier.

Trolley - as mbear said, maybe he would sit in the trolley - it's a bit higher than a pram and he would be able to see more. You can use one in a shopping centre even if you are not going to the supermarket.

Babysitters - can anyone watch him while you go shopping (or out for coffee LOL) so that you can get a break? It might just be that you need to get out without him for now and hopefully once he's walking it will improve.

I hope you find something that works. I know how hard it can be to be stuck at home.