Only allow a connection from specific domains
Solution 1:
Yes, this is possible. You will have to get a list of the IP addresses that those domains use and then add them as exceptions to the firewall.
With /etc/hosts.allow you could try something like
sshd : localhost : allow
sshd : .wavetelecom.com : allow
sshd : .northhosts.co.uk : allow
sshd : ALL : deny
Don't forget to ensure that the hosts in the listed domains have correct reverse dns RRs configured.