Thanks ALL! Great to have some encouragement and useful advice here. I've gone for the Starboard freeride foil board, which I think will make things a little easier when I am able to pick it up in a few weeks. The current loan board I'm using seems to be more of a 'freerace' style board, which I think is a little tricky, but not impossible to use intially. The from foot strap feels too far outboard and slightly too far back, meaning I find I'm sometimes adopting this 'stilletto' front foot position to compensate. I even tried avoiding the troublesome front footstrap entirely and riding with both feet out the footstraps and placed more inboard, which seemed to work once I got used to the 'balancing-on-a-wet-wobbly-table' feeling.
I am improving with each session - I managed over 1km of sustained flight yesterday in ideal conditions. Weirdly, I find everything so much easier on starboard tack, which I find I'm doing longer more controlled flights on, rather than port tack, which I tend to wobble about and do massive crashes on. It must be something to do with dominant hand / foot, etc. When on the slapper, I absolutely hate chop-hopping on port tack, but love jumping on starboard, so there seems to be a bit of a theme here!
Advice about learning to come down under control is a good one. The inevitably competitive side of me means I have been focussing on reaching ever longer flights to exhaustion, so I really must work on finesse things more, rather than just heading for the horizon