1993 Jeep Wrangler Difficulty shifting

My Jeep is in great shape and it runs really well, considering its age. Recently it has become difficult to shift into first gear from a complete stop, and second gear is also pretty hard to shift into. Sometimes if I'm rolling slightly it's a lot easier to get the transmission into first gear. I think the clutch is fairly worn--it engages very high and tends to shake/shudder when cold. I'm wondering if the problem is with my clutch or with my transmission, and how serious it is.