Looking for a very simple drawing app that supports pen sensitivity, suggestions anyone?

Krita(and others) have a complex interface suited for big projects. For some psychological reason, that inability to launch an app and be drawing in less than a second demotivates me to practice sketching. There are some nice simple drawing apps out there, such as Gnome Drawing, but they lack pen sensitivity support which is a no go for me.

Does anyone know of an app that would fit my needs? Of course, being opensource is an absolute must.