Anyone know of any good carpet plants that grow in low tech tanks?
Any answers much appreciated.

The standard response is going to be lilaeopsis mauritiana, but there are probably several varieties of micro swords that will work.

dwarf sag spread out nice before I introduced co2.

dwarf hairgrass and various marsilea spp.

Dwarf sag will indeed spread out - it will try to take over. Don't plant it unless you LOVE it!

Would you know if this would work
Lilaeopsis novae-zelandiae

Thats the old name for Lilaeopsis brasiliensis, and is considered to be a plant requiring high light by most people, unless your tank is very shallow. Lilaeopsis mauritius, (mauritiana) is more tolerant of low light levels, and the common name is micro sword narrow.

Micro sword usually refers to Lilaeopsis, and there is only two species.