My car used to slip like yours when I first had it. Clutch was stiff and notchy and barely needed any pressure on the clutch pedal to cause it to disengage. Oiling the release arm bushes transformed it, much lighter, slippage stopped and the pedal actually needed some decent movement before it disengaged. That was 40K miles ago. I figured the bushes were binding so badly the clutch wasn't fully engaging when the pedal was released.
Nothing to lose trying the oil trick before blowing a load of money on a new clutch if it doesn't improve things.