Question: why the limitation to level 1? Am I missing something?
Because you'd need twice
as many HP to make this work at level 2. So instead of 100 HP you'd need 200 HP.
Is it possible to reduce your effective damage to 0? Get knockback and enough damage reduction to take no damage yourself, then just keep smacking a monster into an IMAWAL wall to fuel Rock Heart, instead of casting PISORF. You lose the Fire Heart charge but are spending far less mana.
Might be doable, and not dependent on being level 1 either. Desecrating TT and Mystera both would probably be the only way to do this. Desecrating TT would let you smack yourself silly with weakening, but that has a minimum of 1 damage. Same goes for Taurog and his attack penalty. Desecrating Mystera would ensure every monster has resistances so that your 1 damage gets rounded down to 0.
As a wizard, using IMAWAL to create a wall costs 1 MP. Busting it with knockback with a rock heart grants 1 MP and 1 HP. With DR (probably platemail) to ensure you take no damage that means you could build up HP that could then be drained into mana by B2P.
This combo doesn't necesistate a level 1 character or obscene health - since the rock heart scales by level and will always maintain the same ratio with B2P. It also needs much less scumming; we just need Mystera and either Tikki Tooki or Taurog on the field (and a third god who is not Pactmaker or Glowing Guardian; we can't desecrate these guys unless we're worshipping someone else)
Also, if you can figure out a way to reduce your max mana, even by 1, you can turn the Transmuter's mana drain into a full MP restore on every conversion.
You could use the strength potion to over-charge the strength bonus. Definitely a good tip. However, as you mention, this is not viable with knockback. You'd need to be using a fireball approach to do this.
I'm still convinced Wizard is the go-to class for an infinite PISORF chain, and the Transmuter is the go-to class for an infinite BURNDAYRAZ chain.