Hi Vasilis, Reboot would certainly give you a head start. It's a great template framework to start with and is based on many months (years?) of research into responsive design.
Much, if not all of the groundwork is done for you.
I'm launching reBOOT v2.0 for X-Cart v4.6.x in November, which is based on the new Bootstrap 3 framework
, includes a plethora of responsive menus and new options. A lot of work is going into this release.
If you have ordered one of our templates in the past, I can give you a discount
Phil