Hey, there is the possibility to scan in your real life sketches if you have no possibility to create them on the pc directly. If you don't own a scanner just take a photo of your sketch and lower the transparency of it. However there is to say that a graphic tablet is almost indispensable when you want to get close to real life drawing and even then it takes practice to get used to, i can tell you from my own experience. Also there are some decent ones that aren't too expensive, especially the ones from Huion can be around 70-80€. With christmas coming up this could work out.

I have never used the program Krita, but in Adobe Illustrator there is a tool called pen tool. It allows you to create lines with the size and form of your choice and you can bend them however you want. This of course pretty much takes away the organic feel that hand made drawings have, but it lets you create really refined lines and overall illustrations.



As Illustrator uses vector based lines you can resize them whenever you want too. There is to say that the Adobe programs or the CC subscription can be pricey, but ... well there are others ways to get the program. Though there should be a similar function in Krita as sceenshots told me.