I debated whether to buy a left side Morsø support, but decided against it. As I remember it was fairly expensive, heavy, and would have eaten up a lot of floor space which I can ill afford.
I echo Dermot's suggestion. Instead, for only a few dollars (maybe $25 or so) I got myself an
adjustable roller stand. It occupies a smaller “footprint” and is height adjustable so you can use it for other applications.
As it so happens, I am using the roller stand at the moment to support a 5 foot x 3 foot frame (for a bathroom mirror) which is too heavy and cumbersome not to sag when using underpinner.
I didn’t get this roller from this company, but from an industrial supply, warehouse catalog. Mine is a wee bit different, but the principle is the same.