Wait, how big of a pot did you end up using? I had the EXACT same issue last summer - my cherry tomatoes were just sad and yellow until I swapped to a 5 gallon bucket with drainage holes. It was like NIGHT and day, they went from barely surviving to taking over the whole balcony. I even had to trim them back because they got so HUGE. The pot size makes ALL the difference for root space in those small spaces.
Did you drill extra holes or just use the bucket as is? I hear mixed things about whether those pre-drilled nursery buckets are enough or if you need to go full swiss cheese on the bottom. Also, what kind of soil mix did you use for the bucket? I tried straight potting soil last year and it got way too compacted, the roots basically suffocated.