yeah, if your pen/screen doesn't support pen pressure, that's gotta be frustrating to work with.
I don't have a touchscreen device myself so I can't give advice there - but there's some pressure settings in krita where you can adjust the width of your line based on factors like stroke speed/tilt/distance/etc., but I personally found them too frustrating to use well myself.
Honestly, if you've got the means and desk space to get a cheaper tablet, I'd highly recommend it. Having tools meant for digital art is going to make the learning curve a lot softer.