Buddleia do tent to take over even after hard pruning, I would suggest something smaller which is also attractive to bees, moths and butterflies and indeed to the human eye.
Abelia may be a good choice (A. grandiflora), it should eventually reach 5-6 feet but when pruned after flowering, it will most likely stay to about 4 foot in a sunny position.
For a tree, I'm guessing you would like something that don't get too big.
I have an unusual tree that seems to becoming more popular, known as 'Wafer ash' (Ptellia trifoliata 'Auria'), mine is only 6 foot, after several years and has lime-green leaves in threes, followed by large wafer like seeds, which in my garden, the birds eat.
Hope this helps - Chip.