Thank you everyone for all the tips and advice - both encouraging and discouraging. My husband and I have decided to give it a go! We were quite reassured by the Dive Instructor who will be with us during the dive that they've brought down divers with less dive experience than us and zero dry suit experience ...and they all managed quite well. (Also quite reassuring that their dry suits aren't the 'super-baggy' looking ones but more form fitting pretty much like wetsuits..I think they're Jetsuit TNG Technicas). And Silfra the dive spot is like one big swimming pool .. no currents with 150 meter visibility, and we will limit ourselves to baby dive depths of just 10 to 20 meters tops. And of course, if at the beginning of the dive, we're really not comfortable with it, then we'll just call the dive off. Many thanks again!