@Deborah ******
I qualified with a pension so I can’t speak from experience about rental income. If I had to guess I would think that they will be more receptive to you having a lot of rental properties rather than just one or two. Just make the best case you can and go with it.
Don’t expect this to be a quick process. You may have to wait it out in your home country or come to Thailand on a different visa and then switch when the LTR is approved. I had to extend my OA another year only to end up switching to my LTR 2 months later.