I would like to introduce a new consonant into Gzarondan phonology,
namely a phonemic distinction between /x/ and /x_w/ (unlabialised
versus labialised velar fricatives).

I'm trying to decide what other changes to make to the phonology in
order to make the new phoneme set look reasonably naturalistic. I
would appreciate some advice.

Intuitively, I feel that if there is a /x/ vs /x_w/ distinction then
there ought to be a similar distinction for (at the very least) all
fricatives and approximates at or behind the velar position. This
would mean adding a /h/ vs /h_w/ distinction.

Alternatively, I could do away with /h/ (but how many natural
languages don't have /h/ ?) and use the /x/ vs /x_w/ distinction in
place of the /x/ vs /h/ distinction. This conserves the total number
of phonemes.

Building on the above approach, I could rewrite history to say that
all unvoiced fricatives once distinguished labialised and
non-labialised forms, but that /T_w/ later became /f/ and /s_w/ later
became /S/, whereas /x_w/ remained as it was.

This sounds reasonable to me, but perhaps there's a better option.

The current consonant phoneme inventory is listed below.

Stops, Nasals & Trills:

/p/  /b/  /m/
/t/  /d/  /n/  /r/
/k/  /g/

Fricatives, Laterals & Approximants:

/T/  /D/
/s/  /z/   /K/  /l/