Please recommend me a flowering tree

[WellTidy]

I would like to plant one each the centre, adds the back, of my square garden. The tree would get pretty much all day sun. Happy to invest and buy something fairly mature. Looking for something that won’t get much more than 5-6 feet across, ideally, but would consider bigger. White/pink/purple flowers, no reds/yellow/orange.

I was thinking a crab apple, but have no idea really.

plant one at the centre , towards the back ...

Magnolia,cherry blossom ?

A small flowering cherry, you'll be able to buy one in flower soon so you can see the colour yourself.

Also don't assume you have to keep it forever: do what the dutch do, as soon as it gets too big sell it on and pop in something new and smaller.

Amelanchiers are lovely

do what the dutch do, as soon as it gets too big sell it on and pop in something new and smaller

We live in a conservation area so once a tree gets big we have to apply for planning permission to even prune it. So we do this. When a tree gets too big to put my hands around the stem, we dig it out and replace it with another tree somewhere else in the garden.

Magnolia "Susan" is the colour you want and it likes full sun, also its size is right too.

Amelanchier lamarkii
You can grow it as a shrub or tree and chop it about.
Lovely white flowers in spring followed by early red berries that the birds love and it's great to watch them eat. Then brilliant coloured foliage in autumn which lasts quite well but then it all drops in a short period of time so no long weeks of tidying up after it.

Fabulous suggestions, thank you so much. I am very excited about choosing something, and now looking for other spots in the garden for dwarf flowering trees too!

Wisteria can be grown as a small tree rather than a climber. Very pretty, fragrant and in your colour scheme.