You were
probably pierced at 1.2mm, so the first size to go to would be 1.6mm
As you were pierced when you were young (like me) then you can start straight away, although if you were pierced by gun (again, like me) then you may have some scar tissue around the piercing.
I'd recommend getting yourself some Vitamin E oil and massaging your lobes with that for a while before you stretch (it's not recommended for use on fresh stretches) then go one size at a time with around 6-8 months between sizes. I personally stretch up every other month.
I use Body Jewellery Shop for most of my stretching stuff, and you can buy both tapers and tunnels on there. Hope that helps