Similar problems with me too, Serendipity! I've got arthritic-type aches and pains, and feel 'wobbly' walking without support. I use a fold-up walking stick for very short distances, and a rollator with a built-in seat for walking any distance at all, but find that a shopping trolley does the same job as a rollator when doing a supermarket shop. I leave the rollator in the back of the car when doing a weekly shop, as it's awkward to get out, and try to park very close to where the trolleys are stored. I can usually get round the supermarket without needing to sit down, but have needed to occasionally. There used to be two handy seats next to the pharmacy in my local Sainsburys, but that's just been closed, so no seats. There were also two after the checkouts, next to the shopping scooters, then there was one... and the next time I went...none. I usually get myself sorted out after the checkouts; rearrange the shopping so I can lift the bags into the car easily, separate stuff for the food bank, put away my cards and receipt neatly, as I try not to be too slow and hold everyone up at the checkout, and can get a bit flustered. So I was quite tired and achy when I couldn't find a chair last time, and rather cheesed off.
A few days before, I'd been to Lidl, using my rollator, as I'd parked there when I had to go some distance to the building next door but also needed a few small items from Lidl too. I found that Lidl didn't have any suitable shopping baskets to put on the rollator seat, they were all far too big, and getting the rollator back in the car and swapping for a shopping trolley was just too much bother. I left in a bit of a strop. So my Sainsbury's shop was the second time that week that I'd found that having just a minor disability can make things so unnecessarily difficult.
So I decided that there was no point in being annoyed, if I did nothing about it, and headed for Customer Services, to politely ask for the seats to be reinstated, please. But saw there was a queue, and was by then too tired to stand, so accosted a lady who looked like a manager, and put in my request for the re-instatement of the seats. I'm not quite sure if she got it. I probably don't look very much like 'a little old arthritic lady' or a disabled person, but as it's not obvious, it needs to be explained, otherwise things won't change was my thinking.
Next time I go to Sainsbury's, I might take a leaf out of your book and put my little old camping stool in the the shopping trolley 'just in case' - though I'm not quite sure if I'll be able to get up from it without some help!
And I think the emails are a great idea. I'll be contributing.