first step in slowing the stretch is to re-pot it the roots are probably getting bound up in that little pot and making the plant think it's in a tight spot and has to compete with other plants for light so wants to stretch above them, this will give you thin stems that don't carry much food from the ground to the leaves
getting them under a proper light instead of just a window sill will make a huge difference, even a 23w CFL
you could do your first top now and get some side stems pushing out, that cutting can be a clone, but that topping will cause it to stretch a little more