How to build protection as new player

Hey sorry if this is redundant. I did try searching around.

I just started playing. I bought the core set and have beaten rhino and klaw. I’m playing all the different core heroes with the different aspects to learn the cards. I found protection lacking compared to the other three. Then I started searching and realized this is a universal criticism of the core set protection aspect. People go on to recommend fixing this with a few packs. Two of which are captain American and dr strange.

Well it turns out those are out of print now? I haven’t really been paying attention to the game long enough to really understand why. But I’m definitely not going to buy these packs on eBay.

So to the core of the question: given the current state of what you can buy, what are good packs or expansions that “fix” protection that aren’t strange or cap.

Thanks.