Hello,
I believe you are describing a situation where you want to NAT the traffic from two different public IPs to two different servers. For that you would need a router that can do either port forwarding or one-to-one NAT. The switch is able to do some layer 3 routing, but isn't really meant to be on the edge, and cannot do NAT translations between public and private addresses. You also won't have a firewall with just a switch.
I would recommend the RV180W, but it looks like your two WAN IPs may be in different subnets, and that usually causes issues with port forwarding or one-to-one NAT for alternate WAN IPs.
Since you want to use two different subnets make sure the router you get is VLAN capable, so you can setup a trunk link to the SG300.
Thank you for choosing Cisco,
Christopher Ebert
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Network Support Engineer - Cisco Small Business Support Center