Kiwi fruit trees want to grow HUUUUGE J, they are also male or female. If you have a warmish indoor space.....what about citrous fruits. Suggest you go to a good GC and ask someone who knows how different fruit trees 'do' in certain conditions. As it sounds like it could be quite pricey to buy a big one in a big pot. Due to all the care that goes into presenting these trees for sale.

I find that most fruit trees tend to do best when planted in the garden but as you want to grow something in a large pot and it can go outside and you have a south-facing aspect, what about giving a fig a go?

It's very tempting, if trying to grow fruit trees indoors, to go for something like a lemon tree, and then to keep it too warm. Indoors for anything like this means an unheated or slightly heated conservatory overwinter where it will get lots of light and not be cooked. Central heating is not necessarily good. If you have a nice, bright conservatory, how about a kumquat tree, if you can find one? Apparently they are relatively easy to keep going, and the fruits are delicious. If you can put it outside in a really sunny spot during the summer months, so much the better. Lots of light is the most important factor.