The thing is it will get ugly whatever you do. Let's imagine a scenario.
Russia decides that since the rest of the world hasn't done an awful lot, it will invade eastern Ukraine on the pretext that there are ethnic Russians being threatened. It turns out that the Ukrainian army isn't quite as crap as Russia imagined, in reality the Ukrainian army is mostly professional whereas the Russian army is mostly conscript. Additionally, the Ukrainians are defending their territory so their army is more "committed" to the cause. The Polish, being friends of Ukraine and still never having forgiven Russia over what went on with the Soviet Union start providing some support, too. Inevitably, just through sheer force of numbers and the bullheadedness of Putin, the Russians begin to overrun the Ukrainians, and their posture is that Ukraine is fighting back so they have the right to keep going until Ukraine stops. As the Russians move west, Poland starts providing actual troops who are now in combat with Russian troops.
Russia manages to push this back though, and decides to give Poland a bloody nose under the justification that they sent troops. Since the west imposed more sanctions, seizing assets of Russian oligarchs, the Russian economy is starting to falter and Putin thinks that the west won't do anything militarily despite Poland being a NATO member, and he feels he doesn't have an awful lot to lose but a lot to gain if he can make Poland fear Russia, so he continues with the intent of crippling the Polish military but not actually permanently invading Poland. However, he's miscalculated, and NATO lives up to its treaty obligations. The US, UK, France, Germany and various other countries mobilize to defend the Polish. The Russian army at the Polish border is rather war-weary by now and is facing well equipped NATO troops and gets pushed back into Ukraine. NATO intends to finish the job and reset the borders to their pre-war conditions, with Ukraine no longer under occupation. They don't have any intent of pushing into Russia. However, Putin is now facing the ignominy of his miscalculation, and decides that defeat isn't acceptable and attacks NATO forces with tactical battlefield nuclear weapons. Many NATO troops are lost, and there are serious civilian casualties in areas caught by the blast on the Polish/Ukrainian border. Now the nuclear taboo has been broken, NATO needs to make sure the Russians can't come back, so destroys a few key strategic targets in the supply chain for Russian troops with tactical nuclear weapons. Russia now feels very vulnerable, and Putin in an effort to scare NATO from fighting further attacks a few strategic targets in the west with strategic nuclear weapons...and NATO replies in kind.
Fortunately a cease fire is hastily brokered before it gets completely out of control, and only a few strategic nuclear weapons are used. But in the meantime, the United States has lost most of its Gulf Coast refining capacity to nuclear strikes (amongst other strategic targets), there are millions dead and a humanitarian crisis in the United States and Europe of catastrophic proportions. Just the injured in the Gulf Coast alone are more than all the resources of the entire healthcare system in the United States can deal with, so the injured are left to fend for themselves. To make matters worse, the Russians detonated a high altitude burst destroying all electronics and communications over a large proportion of North America and Europe meaning just keeping the uninjured supplied with food becomes a challenge due to the loss of working vehicles of all types and the destruction of the electricity grid and communication systems. On top of that, the soot injected into the stratosphere causes a "decade without a summer", leading to poor crop yields to add to the problems of food distribution. Progress of industrial society in Europe, the US and Russia is set back by decades.