Yes it is a pity that 4mm wire is difficult to obtain and 5-6mm would be difficult to bend, might be possible. Or use alkathene water pipe pushed at its ends over sticks/bamboo in the soil, perhaps with small stakes and wires for running string around to hold the polythene down.
The height of my hoops above soil at their centres is about 60cm/2 feet, can be 75cm.
Good that your mesh cover is effective, you could leave it on, because netting also ‘catches’ snow unless the flakes are small and well frozen, which is unusual in GB.
Ah perennial weeds – glad you are getting there too. My couch is much weaker now, field bindweed still going, hedge bindweed much weaker from regular trowelling.