Where is the public key corresponding to my address stored? Some simplified explanations of Bitcoin say, that the Bitcoin address is the public key, and anybody can easily verify that a signed transaction is valid since it was signed with corresponding private key.

But in reality, the address is the hash of another hash of the public key.

So, it's not possible to derive the public key from the address alone.

How do miners obtain my public key, then?
Is the public key included in the transaction I am sending ?
Yes, a transaction includes the public key. So, only when you spend the coins from an address a public key actually becomes public (unless you have shared it with anyone otherwise).

So, as long as you don't reuse addresses, the public key is only known after a transaction, which usually is just a few confirmations away from the address' balance to be 0.