I also like the pomodoro technique but i have a hard time choosing a good looking app. I came across mater from Jason Long [1] but it still need some work under the hood. It is based on Electron.
Which OS are you using? I'm using Be Focused Pro on iOS and macOS. It's a paid application, but it's very refined and can hold nice statistics.
I tracked my progress when I was writing my Ph.D. dissertation, and it helped me tremendously. I can even see the "end crunch" on the statistics, which is very satisfying.
Last, but not the least, macOS and iOS version synchronizes, so when I use my Linux workstation, use the iOS version to keep track of time.
[1] https://github.com/jasonlong/mater