eth_sendTransaction proxy

I'm developing one of the back-end components of my dApp (with web3py). I was using the transact method (contract.functions.transfer(to, amount).transact()) that internally uses the RPC call eth_sendTransaction. When using this method thru services like Infura, I get an error: The method eth_sendTransaction does not exist/is not available. This totally makes sense since eth_sendTransaction sends the transactions without any signature and Infura doesn't hold the keys. The solution that works is signing the transactions first and then using eth_sendRawTransaction.

But all this made me think if it doesn't exist a package that can provide an eth_sendTransation proxy. This proxy will receive unsigned transactions (from trusted sources), it will sign them and resend them as raw to the underlying service (example Infura).

The main advantage of a design like this one, it's my private keys are only present in the proxy process, that's a minimal component that can be better audited. And in my origin process (a complex beast that might be a django process, with many dependencies and different end-points, potentially hackable), I don't have access to the PKs.

Does it make sense to do a setup like that? Do you know any tool that does this or a project that can be used as starting point?

Or, much better, this can be a service provided by OZ Defender. With filters not only indicating the source of the call but also the transactions allowed to send.