A reaction that I have on another card is:
"When you would gain a card, you may reveal this. If you do, instead, gain a cheaper card, putting it anywhere in your deck."
It could work on this card. This card can't trash curses, but it can block them, and it has a nice little bit of self comboing.
That was Partition, wasn't it? I generally like many of your ideas, but i don't think that Reaction is a good idea. On some decks it just gets too absurd. Remember Cache/Trader/Partition/Squire/Watchtower/Cultist/Goons... If you have WT, Partition and Trader in hand when somebody plays Cultist, it's gonna be horrible...
In order for anything crazy to happen, you need:
Trader+Watchtower+Partition, all in your hand and Squire in supply. You'd also need something crazy for Squire to turn into, or something cheaper than that attack card. It's all very specific, and I think it's more a cool consequence than anything else.
Mind you, I also had this idea for a reaction (or duration effect):
"When you gain a card other than a Silver, you may reveal this. If you do, gain a Silver."
Of course, Partition breaks this. That reaction is too similar to Trader anyway, so partition is the go.
I think that the top effect of that card though (Trash a card. Gain 3 differently named cards that each cost less than it.) is too niche. This effect is also niche, but at least there are useful situations for it throughout the game, and the reaction synergises with another copy of the card.
So then, I think my "final version" will be:
Overhaul
Action/Reaction - $3
Trash a card from your hand. Gain a card that shares a type costing up to $4 more than it.
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When you would gain a card, you may reveal this from your hand. If you do, instead, gain a cheaper card, putting it anywhere in your deck.
(NB: Due to the lose track rule, if you put the gained card anywhere but the top of your deck, you can't "chain" the reaction)