I wouldn't disable DHCP unless you dont mind setting up a static address for anything that connects to your network.
If you want to keep it disabled you must edit the connection properties and hardcode your
address , gateway , dns servers etc. on every device that will connect to your network.
Otherwise re-enable DHCP, as before, and just change the range so that you new router's IP is not in that range. Most people can get away with a range of 30 ips. or less. Even me, and I've got 2 media streamers, printers and laptops with multiple interfaces all clamouring for IPs.