I would like to use Express instead of Standard. Does Express still have the annoying habit of going to sleep if left unused for a period of time?
No, it does't, and never did.
The post you link links to the blog http://blogs.msdn.com/b/sqlexpress/archive/2008/02/22/sql-express-behaviors-idle-time-resources-usage-auto-close-and-user-instances.aspx that explains that the 'instance going to sleep' is a RANU behavior (user instance), not an Express behavior. As you plan to move from Standard to Express, is obvious that that you do not plan to move to user instances (RANU).