It is Putin's hope that, with time, the West will get tired of propping up the Ukrainian military and throw in the towel. The best way to deter future Russian aggression is to prove this is not the case, or, if Ukraine does fall, to make sure the Russian people continue to face consequences after the last bullet has been fired. Here are some low-cost measures we could take to render more help to Ukraine than we are currently giving them:
#1. Wartime use of friendly soil
Russian POWs captured by Ukraine should be held in European prisons, and preferably guarded by Western personnel so that the Ukrainian manpower tied up in keeping them from escaping could be reallocated to the front lines. More importantly, it would ensure that Russia doesn't automatically get its POWs back by conquering Ukraine.
On this note Ukrainian should be allowed to set up armament factories in, say, Poland or Romania so that the good work of making defensive weapons can go on unimpeded by Russian bombs. Of course, they shouldn't be allowed to use these weapons before these have been shipped to Ukraine first. Ukrainian drone pilots should also be allowed to work from the safety of Europe or the United States, if this is practical. Finally, Ukrainian weapons that won't be used for a while should be kept under the safety of Polish or Romanian soil until such a time that they're needed again.
#2. Call Russia's Bluff
Ukraine should be allowed to use any weapon in its arsenal against military targets on Russian soil, regardless of where those weapons came from. Russia's been drawing nuclear red lines in the sand for the better part of the last 3 years, and every time that Ukraine crosses them nothing at all happens. Russia's existence virtually by definition cannot be threatened in this war, because Ukraine is weak and because Ukraine would be willing to make peace with Russia at any time, assuming they get their territory and people back.
#3. Contingency Plan
To signal to Putin that even conquering Ukraine won't spell an end to his troubles, the US and its First World allies should sign a treaty codifying into law this pledge: that a Ukrainian government-in-exile, if the country should fall, will be diplomatically recognized for at least 40 years after the fact, and that no sanctions levied against Russia during the war (such as the oil price cap) may be lifted unless the Ukrainian government, be it the current one or a government-in-exile, consents to a peace treaty first. This entity would also receive the necessary funding to sustain basic operations for 40 years, and its employees and leadership will be allowed to stay in a Western country.
Russian POWs, likewise, would never be released without the permission of the Ukrainian government-in-exile in this event, even if this meant their imprisonment for the next 40 years. Since these men are war criminals who invaded a peaceful country, and have probably committed murder in doing so, this outcome wouldn't be unjust. In the US it's not abnormal for a murderer to spend 40 years behind bars.
#4. Olympic Games
Related to #3, the West should pledge to exclude Russia from any Olympic games hosted on their soil, or boycott any Olympic games held elsewhere which does not include the restrictions placed on Russia in 2024, in the event that the war continues without a peace treaty which the Ukrainian government, be it the current one or a government-in-exile, consents to. The 2028 and 2032 summer Olympic games will be held in Los Angeles and Brisbane (Australia), respectively, while the 2026, 2030, and 2034 winter Olympics will also be held in Western countries. The bloc of countries which agreed to the aforementioned treaty should also clench the 2036 summer Olympic games and the 2038 winter Olympic games at the next round of bidding so that there's no chance of Russia participating before 2040 at the earliest, unless Putin agrees to peace with the Ukrainian government.
#5. Denmark
Denmark ought to permanently suspend passage through the Danish Straits for all Russian Navy ships. Furthermore, it should impound and ultimately seize Russian vessels identified as part of the "shadow fleet" which skirts the $60 price cap on oil (much of this activity begins in the Baltic Sea and passes through the Danish Straits). This is probably legal where proven through stuff like satellite imagery that said vessel has sold oil either directly or indirectly to countries party to the cap, including all EU member states. Since much of this fleet is uninsured, losing just one or two vessels could be a huge blow to the fleet's profitability.
Again, these terms ought to be enforced for so long as the Ukrainian government, be it the current one or a government-in-exile, has not signed a peace treaty with Russia.