Outside mirror

Not really a Cal Look question, but the '58 I have just bought does not have an outside mirror. There are no other old VWs around here for me to look at, so can people advise me whether round or oval shaped mirrors are better to use. I notice from looking at photos that Bill S changed from an oval shape to round at some time and I wondered whether this was for looks or whether the round mirror gives a better view. I'm not feeling too confident on the motorway without one!

Also, all the round mirrors I have seen on the net seem different to Bills as the arm mounts centrally on the back of the mirror, not offset...anyone know where I can get one that is offset?
Thanks

Richard

Bill's car....

Mine...