Agree on a torsion axle. In my opinion, a leaf spring axle on a small, lightweight trailer is a step down in terms of ride quality.
You have some torsion axle choices to consider, ranging from least cost to highest.
(1) A Dexter #9 axle or equivalent, max. rating 2200#. It can be ordered with 7" brakes
. That would be closest to OEM.
(2) A Dexter #10 axle or equivalent, max. rating 3500#. It's a sturdier axle and can be ordered with 10" brakes
for more stopping power. It can be de-tuned at the factory as low as 2500#, which would probably give an acceptable ride with a Trillium.
(3) A Flexi-ride axle, which has the ability to change the axle arm start angle to increase or decrease the ride height depending on conditions.