My suggestions for your stage of development would be
(1) Studies
LEE 12 Studies, Op. 31 (IMC) - for developing slurred legato bowing
STURM 110 Studies, Vol 1 (IMC) - short, musical, like orchestral difficulty
KMENT Elementary Studies for Bass (Hofmeister) - don't be put off by exercises in keys with lots of sharps and flats near the beginning!!
SLAMA 66 Studies in all keys (IMC)
ORCHESTRAL COMPLETE PARTS (Zimmerman) and listen to recordings of the music
IMO Simandl (Gradus ad Parnassum) and Findeisen are morale destroying unless you enjoy musical marathons with self-inflicted pain for dubious benefit. Stick to exercises that are stretching but playable, that move through different keys, rythms and speeds, and that ask for dynamics and expression/phrasing. For these reasons I push Sturm on my students.
(2) Pieces (with piano) - in approximate rising order of difficulty
S/SAENS The Elephant - try two different fingerings in the middle section?
GALLIARD Sonata (2nd & 3rd Movts) (IMC) - 16th. note passages to play powerfully
MARCELLO G Major Sonata (IMC) - slow=expressive, fast=technical
HESTER The Bull Steps Out (Yorke) - in Ragtime, slurs notes differently for style
VIVALDI Sonatas - I like No.3 and No.5, again slow=expressive,fast=technical
ECCLES Sonata (IMC) - 1st two movts. are great but 3rd difficult at speed
CORELLI Sonata (IMC) - lots of hopping around in 2nd.Movt.
CAPUZZI Concerto in F Major (Boosey&Hawkes)
BACH 6 Cello Suites arr. for Bass (Peters)
Cheers.....
DP