If it hasn't changed, you need to take the commercial written and atp written as well as the commercial checkride and atp checkride. They can be done in single and multi engine aircraft. No need to do it in a simulator unless you want to.
As far as schools go, it's up to you which one fits you best. For conversion, I would recommend the bigger, well known schools as they usually do it in as little time as possible. Just my 2 cents.
VF