Processing bitcoins on my website completely by myself, with no third-party bitcoin SaaS services I want to be able to accept and process bitcoins on my website only by mysefl. With no 3rd party bitcoin services. How can I do that? One way is to use Electrum. But its documentation regarding merchant is really bad. Does anyone have experience with that?
It doesn't have to be Electrum, though, and any bitcoin software will.
I'm a programmer, I'm ok implementing a neccesary part, it if I have to, by myself.
First, Electrum relies on Electrum servers, which are essentially a third party SaaS for SPV proofs. It's a fine thing to use for most people and as long as you aren't concerned that the server may compromise your privacy, you should be fine. But that said, you can say that about any SaaS service, so Electrum is probably not the solution you're looking for.

If you want to do everything yourself, you will have to run a full node at a minimum. You can create a wallet using a library like pycoin (https://github.com/richardkiss/pycoin) but that's much more work than using a full-node wallet like Armory.

There's actually webshop code written for processing bitcoin payments yourself (https://github.com/goatpig/BitcoinArmory/tree/master/webshop). The main benefit here is that only the public key is on the server so even if you get hacked, your bitcoins can't move without your say-so. Full disclosure: I wrote that code.

Another option may be using bitcoind, but that will require you to keep your private key on the server (NOT A GOOD IDEA).