I see the app uses much sliders for measurement items and symptom severity.
While sliders look nice, I personally prefer a row of nice buttons with numbers in it. Simply because it works quicker. The quicker all things work, the better I’m willing to track everything and the more I benefit from the app.
a row of colored (color orresponding with the severity) buttons with the number in it.
Both. Slider and buttons.
Let the user choose / configure what they prefer.
Make the slider ‘clickable’. Now one needs to slide from the left to right. If I want to set it to 6 it is more comfortable to click halfway and slide it a little to left or right until I have the 6 I want.