On the FCO page for Ukraine, the guideline says that is needed the proof of vaccination, PCR or LFT, and travel insurance.
In addition, for people coming from the UK one extra rapid test will be performed at the airport before the controls, because England is one of the countries with the highest rate of Delta variant.
To sum up, I booked the hotel and I will buy the flights (about 20£ A/R) but the chances I'll go are 50%.