Galaxy S4 mini; lost on installing CyanogenMod 12.1

Hello there,

before getting into details: I am pretty new to the whole business of smart phones; so, if my request doesn't fit here ... please don't get too angry with; but tell me where else I could turn to.
In case this is a good place to ask my question; here we go:

I recently acquired a S4 mini (GT-I9195); currently runing Android 4.4.2; build number KOT49H.I9195XXUCOE4; and as subject says: I want to install cm 12.1; and I am getting nowhere.
I started with this wiki page wiki.cyanogenmod.org/w/Install_CM_for_serranoltexx
The wiki says:

• Use heimdall to install the CM recovery image


• Then, use that recovery image to install the actual CM build

And well, I am already failing with step 1.
My computer is running ubuntu 14.04; I first installed heimdall from the ubuntu repositories; and when following the instructions; I ended up with
heimdall ERROR: Failed to receive PIT file
Then I fetched the latest heimdall source from github; compiled ... and ran that; but result wasn't much different
heimdall ERROR: Protocol initialisation failed!

Then I tried to do everything with AndroidStudio / adb / fastboot.
I enabled USB debugging within the mobile phone ... and I could actually start an adb shell. I could also use adb to boot the S4 mini into recovery/download mode.
But when I do a "fastboot devices" then ... no devices are showing up at all.

I don't have a windows system; so I tried to get my VirtualBox windows to get it "talking" to the phone; maybe in order to use Odin instead of heimdall; but no luck there.
( I thought about using twrp ... and the wiki pages there basically talk about using Odin on windows)

Long story short: I am looking for the "easiest" way to get CM 12.1 on my S4 mini; preferably without rooting; and low risk of bricking ...

Download from this link