It appears that there is a worldwide shortage of elastic - due, no doubt, to all the masks being created, so this is the alternative fastening on my prototype mask. I have watched several YouTube demonstrations with a variety of methods and fastenings, from cut-up T-shirt to home-made tapes, so there is much choice available but I am not prepared to try them all.
This is the first one, unpicked to remove the original elastic that proved too wide for my dainty wee ears. reconstructed with tape, as suggested by annjohn yesterday. I did not waste the narrower, more suitable, tape (being still at the experimental stage) as I have more of this wide one.
Then we just have to choose our favourite fabric out of the selection to hand and get busy - who knows, we might not actually need any of them.