sounds like the syncro rings are worn, try speaking to bernie , other thing to try is double clutching, ,ie as you come off the throttle dip the clutch as you put the lever from 1st to neutral, then quickly release and dip the clutch again as you engage second. Feels dead slow at first, but with practice its dead smooth and quick , and makes horrible boxes change well
do you have probs coming down as well, i.e 4th to 3rd etc etc? if you do try to match the revs to the lower gear,using heel & toe as you down shift, much smoother and much less wear on the box