Well, lets begin with the fact that Kyiv isnt in Bulgaria.
Now your question. I've only been to Kyiv a few times so I'm no expert, and my travel style and accommodation preference may not be like yours. On my trips I have stayed at the Senator Maidan https://senator-apartments.com/ and on one occasion i stayed at the Hyatt Regency for a night on a one night lay over (not impressed). Again, my experience in the city is pretty limited. I could spend weeks there and not have a great understanding. Its that interesting and that varied.
For the next trip (probably in the fall) I will either stay at the Senator again or draw a line from The Hotel Ukraine to the Hyatt Regency and then find something one or two block on one side or thee other. The area is full of recent and ancient history and you could spend several days there alone.
Another place that interests me for accommodations is along Khreschatyk St at, and just south of, Maidan. (Maidan Nezalezhnosti, in English Independence Square). Lots of restaurants, clubs, nigh life. Weekends sometimes they close the street and make it pedestrian. The area has great Stalinist Imperial Architecture (not to be confused with Soviet concrete block houses). Did you know that there are 3 types of communist architecture and some of the best of each is in Kyiv. The Hotel Ukraine is a perfect example of what happens when a building is in mid construction when views on architecture change (Stalin's Imperial style to Khrushchev's brutal minimalism). Great building if you are into architectural history.
Before you go you have to watch on Netflix "Winter on Fire" and "Servant of the People". The first a tragic documentary, the second a comedy worth seeing for the opening scene where the oligarchs are standing on the roof (or a balcony) of the Hotel Ukraine looking down on Maidan. Its hilarious too..
You dont sound like a guide sort of person, but if you need one I know an amazing one.
A quick spelling lesson. Kiev is the Russian spelling for the city. Naturally while under Russian occupation, Russian was pushed as the language of choice and Kiev became the norm. To this day if you go to Google Flights for instance you had better put in Kiev if you want to search. The preference in Ukraine at the moment is to adopt the Ukrainian spelling; Kyiv. Odessa is Russian, Odesa is Ukrainian. The Ukraine government and the US government now recognize the spelling as being official. This is interesting https://www.rferl.org/a/ukraine-kyiv-kiev/28478117.html
Okay, it's not a big thing for a tourist, but I love little facts about the places I am going.