All of these recommendations are based on android/fdroid:
Bodyweight Diary: Trale https://f-droid.org/en/packages/de.quantumphysique.trale/
Workout Log: GymRoutines https://f-droid.org/packages/com.noahjutz.gymroutines/
Calorie Counter: Energize https://f-droid.org/packages/com.flasskamp.energize/
Breathing Techniques Breathly https://f-droid.org/en/packages/com.mmazzarolo.breathly/
Ive been meaning to flash this onto my fairphone but the websites instructions are a bit confusing (I've installed calyx, eos and graphene on other phones)