WordPress 3.4.. vs 3.5 themes

I would like to make a new website, using a new premium theme. Im afraid that the theme will have some problems running with 3.5.

So is there a way to get the older version, and then make the website. Untill the theme gets a update and its safe to update to 3.5?

Reason for this is that after updating to 3.5 a lot of my current websites seem to be having problems.

Also, i dont like to use ftp, because i would like to instanly see my results on the website. How can i get 3.4.. and do this?