I have been looking at:
noip.com
zoneedit.com
but I am not sure if they all do what I want?

Basically I am having problems at my host and do not want to move my site yet, so I want a way to insure that I still receive my emails.

From what I have read, I created this outline of what needs to be done.
choose a service
create dns zone
add secondary mx for email

login to the domain name registrar
add dns zone to domain name ns servers at registrar

login to the hosting server
Edit your DNS server to allow zone transfers to the backup DNS server

Zone "mydomain.com" {allow-transfer {1.23.456.789;};
notify yes; also-notify {1.23.456.789;};

login to the backup DNS server
Configure your master IP in the backup DNS server interface
enter the IP address of your master server
Verify the zone transfers works using dig
Dig @yournamserver.com mydomain.com SOA +short

login to the hosting server
Update your zone file to include the backup DNS server (NS) records

questions
Is the outline above complete or is anything missing?
Where to point addresses to?
How does the dns service check to see if the hosting server is down?