So Electrum is my best option in this case? It has a built in feature and is a pretty old and known wallet. Also, as always in a safe environment.
Electrum or Bitcoin Core are probably two of the most well known and developed wallet. If you're sure that you can operate your wallet in an environment that is safe and secure, there shouldn't be any problems whatsoever that concerns security.
Your idea for signing message should primarily be proving the ownership of the address. Signing a message will prove that they are in ownership of the address and whatever amount of Bitcoins associated with that address at that point in time. You should be clear about the message and the context, specifically taking note of the purpose and the timestamp within the signed message.
I appreciate your thoughts, What should be an ideal message example? Something like this maybe? Do take into consideration that I'm the one to request it and verify it. Nobody else involded.
Message: "Bitcoin Signature for Proof of funds "
Signature: H5g/Jc...<...>...P6Ty5=
Timestamp: 2024-08-22 15:00:00
As for the verification part, since I'm acting as third party verification, Verifying should not be of any trouble as well? Still doable on Electrum. In this part, I would need an address, a signature and the exact message. The valid signature pop up should clear any concerns regarding ownership.