No NATO membership is an obvious suicide pact.
If I were King of the World:
I think they could propose allowing Ukraine into NATO, but with limits on how many non-Ukrainian NATO troops could be in Ukraine at any one time - like 1000 or so. Enough for training and logistical support, but nowhere near enough to invade Russia. No nuclear weapons in Ukraine - but it still gets that mutual defense safety.
Perhaps sharper limits on how many non-Ukrainian NATO troops could be east of the Dnieper at any given time. Those limits would be tied to Russian adherence to other aspects of the agreement. Russia breaks the rules, NATO gets to add more people.
Russian
and Ukrainian forces pull out of Donbass and separatist militia are disarmed, UN peacekeepers go in. Both districts get divided along the 2014-2022 line of control, with UN supervised independence referendums on both sides of the lines of control. Real, free referendums with no Russian interference.
Russian citizens who didn't live there pre-2014 don't get to vote in that, but Ukrainian citizens who lived there pre-2014 do get to vote even if they have not lived there since. That could result in the separatist-controlled areas staying separate, in which case Russian troops could re-enter them, subject to limitations on numbers and weaponry.
If the referendums go in favor of staying in Ukraine, then Ukraine gets to send troops back in. The U.N. peacekeeping force would be inherently temporary, although U.N. observers could be permanent.
Crimea stays Russian, Ukraine delivers water to it. Russia pays for it.
A lot. A big fat check every year for decades, a mortgage payment on the purchase of Crimea and for water delivery. Limits on the number of ground forces Russia can post there - it's a Navy port, not an Army base. Ukraine gets free access under the Kerch strait bridge, everyday forever. Russia can't use training exercises or security concerns as a pretext to block Ukrainian access - ever.
Allow Russian to be an official language. Schools can teach in it, it can be used for legal proceedings. That said, nobody should be forced to be taught or do court and legal proceeding in Russian. As a Yankee, I struggle with this - English is the
de facto official language of the U.S., but does not appear to have any legal standing in that regard. English as the Official Language is a political issue here. I'm not totally certain how official languages work, other than some level of recognition in the development of school books.