Thread spools.... You want the windings close to the armature.
Small diameter spools might be okay but every mm between windings and armature takes away effect, the fall-off is fast. For some bobbins you would be better off with cardboard or rolled card stock and tape.
Here they make strong solenoid and measure move force vs hold force.
Adding: and of course you put a capacitor across power and ground at each coil and I think a diode, all for circuit protection, right? ULN28xx Darlington driver chips have that built-in btw.