Hey, just a heads up, but Adrix & Nev and Mondrak (and any other effects that care about a token being "created") won't work with the 6th Doctor. Tokens that are the result of copying a permanent spell aren't created and won't trigger those sort of effects. It rule 111.12 which you can find in my deck's description (link below).

Other than that, you seem to be on top of the other ways to abuse the Dr, so I guess if I was going to suggest 2 cards for replacements... Galadriel, Light of Valinor is absolutely nuts when you have 2+ of her. Sigarda, Font of Blessings isn't quite as good as Shalai, but like her, getting 2+ copies means they protect one another (along with all your stuff) from any targeted effects.

Feel free to check out my deck for ideas. Upvotes on any of my decks are appreciated. Dopplegangbangers - Historic Flash Convoke Copies

Hey, just a heads up but you have a few things going on here that don't work within the rules like you want them to.

First off, your commander pairing actually doesn't work together. The Doctor explicitly states it triggers only once per turn so "triggers an additional time" effects like Clara Oswald and Roaming Throne won't cause the 6th Dr. to trigger again. You're after effects that copy his trigger or that copy his tokens after the fact. Twinning Staff, Strionic Resonator, Errant, Street Artist, and Esika's Chariot are all examples of the different things you CAN do in your colors that work with your Doctor. See my deck's description for more.

Second, Doubling Season and any other effects that care about a token being "created" won't trigger from the 6th Dr's. tokens. Rule 111.12 (see my deck's description, link below). Basically, a token that is the result of copying a permanent spell (6th Dr/Lithoform Engine's bottom ability) aren't "created" and won't trigger abilities like Doubling Season.

I personally run Peri Brown as my companion, but my deck should help with some great budget options even if you stay blue/green. Upvotes on any of my decks are appreciated. Dopplegangbangers - Historic Flash Convoke Copies

Hey, just a heads up, but Clara Oswald doesn't work with The Sixth Doctor. You can run effects like Strionic Resonator that copy his trigger but "triggers an additional time" effects like Clara and Roaming Throne unfortunately don't work because of the way the Dr's trigger is worded.

I personally run Peri Brown as my companion to get the same colors and the convoke is honestly just amazing here (especially with Flash enablers).

Feel free to check out my deck for ideas. Upvotes on any of my decks are appreciated. Dopplegangbangers - Historic Flash Convoke Copies

Hey, just a heads up but Anointed Procession, Adrix and Nev, Bennie Bracks, and any other effect that care about a token being "created" don't work with The Sixth Doctor.

Rule 111.12 (in my decks description, link below). Basically it boils down to tokens that are the result of copying a permanent spell aren't "created" and won't trigger the above effects.

You're after effects that copy the Dr's trigger (copy specifically as "triggers an additional time" like Clara Oswald/Roaming Throne won't work here either) or that copy his tokens after they've already entered. Twinning Staff, Strionic Resonator, Errant, Street Artist, Romana II, City of Death, Esika's Chariot, Lithoform Engine, and Second Harvest are your best options here.

Feel free to check out my deck for other ideas. It's not superfriends but it should still give a few more ideas (and rule 111.12). Upvotes on any of my decks are appreciated. Dopplegangbangers - Historic Flash Convoke Copies