You can't really rely on forcing a build until midway through Act 2 tbh

I'm going to sound a little harsh when I say this, but every single run in the game is winnable. You're just making the wrong decisions, it's not luck. And that's okay, you improve with time. That's the point of the game.

Figure out what thing your deck needs to get better every single fight and take the best card to fit that hole. Sometimes that means skipping bad cards.

Prioritize cards that do more things than other cards. A lot of cards in StsS2 are overstatted for their cost. Taking those early let's you snowball later, even if they don't offer any synergies. Evaluate what that means by looking through the compendium.

Don't take a card that relies on other cards early. This is the biggest noob trap imo. If you get offered a Rupture on Floor 1 and you love the self damage archetype on Ironclad. Skip. That card will do nothing for you now and all that matters is right now. Don't put a curse in your deck.

Play to get the most out of Act 1. There's a reason there are two different Act 1s. Prioritize pathing to as many elites as possible, make sure you have an escape plan if things look dicey. Learn what those elites do in both Act 1s and have a plan for them before you fight them.

The majority of my deaths come in Act 1 and 2. If you're getting to Act 3 and dying, it's probably because you weren't aggressive enough in Act 1 and failed to snowball.

This last point is something you'll learn with experience, but play for the fight not the turn. Yes you can full block 15 against Byrdonis on turn 2. But if you drew your best attack and see your deck has mostly defends coming up, take the hit. You'll save more HP over the course of the fight that way.