Sounds like you don't need another network, just more bandwidth from your ISP. That would be a question for them if they can increase your bandwidth.
If you get a second ISP, you will need a router that has load balancing (basically two+ internet ports)
The other way would be to treat them as separate networks and get a modem/router from each ISP. WiFi can be an issue here since they would be in close proximity on the same frequency. If they offer 2.4Ghz and 5Ghz you can turn on or the other off to keep them really separate. If they are both 2.4Ghz then you would want to change the channel they broadcast on. IDs 1-12 usually, commonly defaults to six, you don't want both on six.