What Does a Ukraine Peace Deal Look Like?

Russia's war against Ukraine has begun in full force. So far, the Ukrainian government and people have done a remarkable job in slowing Russian aggression. But Russia is much bigger than Ukraine, and every day this war goes on is another day of wholly unnecessary death and bloodshed.

There are reports that Ukraine has asked Israel to mediate peace talks with Russia (Israel being one of a very small number of countries that remains on at least halfway decent terms with both nations). Obviously, if Israel can do anything to bring this horrific war to end I hope it does so. We also, unfortunately, know that what with Israel being, you know, Israel, any hiccups in the negotiation process, or any sense that a resulting agreement is unfair or unjust (and someone will always find it unfair or unjust) will yield a quite ... predictable sort of discourse as a consequence.

Which leads me to ask: what, even roughly speaking, does a peace deal between Russia and Ukraine even look like?

This is an area I want to emphasize I am no expert in, and so I invite people who are experts to correct or supplement me. But here are some of the assumptions I'm working off of (which, again, I'm very open to correction).

1. First and foremost: this was a complete and unprovoked pure war of aggression by Russia against Ukraine. In a just world, they should get absolutely nothing -- not Donetsk, not Crimea, not Luhansk, nothing but a barrelful of summons to an international war crimes tribunal.  Any end to the conflict which appears to reward Russia for launching this invasion will be hideously unjust. Unfortunately, the ends of wars needn't be any more just than their beginnings.
2. While Ukraine has done an impressive job stymying Russia's advance so far, in terms of pure military material Russia retains a considerable advantage. It is highly unlikely that Ukraine can actually push Russia back on the battlefield or force Russia into a position where it has to "surrender", even though it can inflict heavy losses on Russian forces.
3. Ukraine is in a bit of a paradox: it obviously wants the war to end as soon as possible, but it's only chance to prevail is in slowing it down -- putting Russia in a morass, making the price unacceptable for the Russian people on the home front.
4. The war has not gone as quickly or as smoothly as Putin predicted, and that's a big problem for him. Europe is far more unified than he expected, his military is underperforming, and his normal allies are saying "nuh-uh, this is your mess". He needs something to come out of this that he can point to as a win, and undoing western sanctions that only came into play because of his own recklessness won't cut it. Launching an obviously optional war of aggression and limping back in pure defeat potentially puts his entire regime in jeopardy. In this context, it realistically puts Putin's head in jeopardy.

Basically, the core of the problem is that a viable deal almost certainly needs to give Putin something face-saving, but there's nothing obvious to give him that would not rightfully be a non-starter from the vantage of Ukraine and which wouldn't set a horrible precedent in terms of incentivizing offensive wars of aggression. Now to be clear: I, personally, have no interest in saving Putin's face or any other part of his body. He can swing for all I care. But while Ukraine can perhaps stop Russia from achieving total victory, it can't force Russia into a position of abject defeat, and so cannot compel a deal that -- however just -- Putin will never accept and can never accept without probably being ousted from power outright.

So that's my question: under these constraints, what does a peace deal look like? What proposal can be put together that maintains Ukraine's territorial integrity, deters Russia from undertaking similar actions in the future, but actually can get Russia's signature? If such a deal cannot be contemplated, it is hard to see how this war can be prevented from dragging on for the foreseeable future.