Spring supports might help with pitching but it is really down to damping. Either upgrade/renew the shock absorbers or adjust the nose weight to remove the resonance between the pitching frequency of the trailer with the damping frequency of the car's suspension. Spring assists are typically to prevent the suspension from sitting too low when loaded, hence reducing the available stroke of the suspension and increasing the chance of bottoming out.
The combination of trailer load, length, drawbar length, load distribution, tow-hitch-to-trailer-axle length, tow-hitch-to-car rear-axle length, suspension spring rate, damping rate, trailer CofG, stabiliser friction and so on will affect the pitch and sway behaviours. I'd try to adjust the easy ones first before getting hands oily. I always used to run a nose weight of around 75 kg and never had a wobble or wag. Set with a piece of wood and bathroom scales!