@nogbadthebad Thanks. I got it working with only a few steps, without any routing. Just create a new tunnel, new peer, new interface, and a new vpn gateway, based on setup config obtained from vpnunlimited. Then just create a firewall rule to allow, in my case, a whole subnet address to access all via the new vpn gateway. The chosen subnet belongs to one ssid I created just for Wireguard vpn connection.
I will write a more detailed instruction and post it here very soon.
Update: I've just posted my more detailed instruction here:
Instruction-WireGuard to VPN Provider only for a specific subnet