What is a recommended firewall for a small business?

Our network and domain is pretty small. We took over a retiring business and are trying to restore the network.

The network looks like this: Main ISP Wireless Router > 5-port Switch (this mini switch splits to another network segment for another isolated office) > 15-port switch for our own internal network.

The ISP wireless router has limited firewall capabilities. Is there any true FW device you would recommend (that is fairly easy to configure)? Based on my knowledge, the FW would need to be placed in front of the 15-port switch. I’ve looked at Cisco Meraki MX86 and it seems straightforward.

Thanks!