Unfortunately, that user is no longer with us. You can stick with any reputable wallet nowadays, and it supports double-spending with RBF.

That is not possible, and it never was in the first place. When your transaction has 0 confirmations, it is by the protocol not final. If you're referring to the mempool policy rule before full RBF, then it is neither possible. Almost all nodes will have upgraded to Full RBF by now, and even if full RBF nodes are a tiny minority, it's enough to reach the mempool of the mining pools.