ok, ive gone through the time consuming process of creating a yahoo
account and joiing this group just so i can answer your guestion.

I dont know how grading systems work where u are, but here you go to
Grade 8 and after that u go above grade and for a diploma-fellowship.

anyway, try the puncinella suite by stravinsky, its really nice to
play and it'll let you play around with the thumbs position, which
is always a good thing seeing as its all about showmanship these
days :).

If your having trouble finding it, I suggest picking up a copy of
Double Bass Solos 2 by keith hartley, its in there along with some
other really nice pieces

hope ive helped