There will be someone more mechanically minded than me come along shortly, but I’d be looking firstly at the clutch slave cylinder. I’d suspect that when it’s warmed, it’s not retracting fully, so not fully engaging the clutch to the flywheel. It’s a quick and easy-ish part to replace… and a lot cheaper than a whole new clutch kit!!
If you can give some details of your issue, I might be able to advise?
I’ve replaced every single component in the clutch assembly, from the pedal itself to the cylinders (twice), clutch line(s), fork, pivot pin, fluid (lots), release & pilot bearing, clutch assembly, flywheel. Even made my own master cylinder gasket from some Flexoid cardboard stuff just because.
I am now slightly clued in to the workings of the system, if you can believe! There are a good few flaws in how it operates and things that do fail relatively commonly.
Have you had any work done to it recently? What’s the symptoms, year, miles etc?