Could you write up an article on how to go about this whenever you get the time?
I've looked at wireguard and openVPN configs but can't understand how two different VPN sessions can bond/unbond data packets over two different connections without some serious enterprise grade hardware + software.
Another option is to buy a single IP or rent it from your single ISP, and then BGP that to the world while being on a CG-NATed internal pool from the same ISP. Not exactly a bulletproof failover solution since it's the same ISP, but akin to the expensive multipath option offered by Airtel / Tata.
This option too needs two pieces of hardware at local level and ISP level to split and recombine the packets, so we're talking collocation space at the ISPs data center.