Time to go back to basics, starting with the way you sit and stand to play. Make yourself comfortable then bring the bass to you (I always try to have an imaginary arrow pointing from my chest to the bridge and the nut about level with the top of my ear). Then bring your LH up from your side as naturally as you can reach for, say, 1st. position from a gentle fist so that your arched fingers and slightly bent thumb form a letter "C". Observe how much strength is needed to press the string to the fingerboard with all four fingers, only enough for the sound to pop out cleanly if you bow while pressing down gradually. Or hear a click as the string hits the fingerboard.
With the bow follow Michael Klinghoffer's suggestion and balance the bow (held up in front of you) on your R thumb, then oppose it with the second finger and drop the other fingers into place (see his ten lessons on Youtube). Finally slide the hand down the stick into the usual bow hold. Still holding the bow drop your hand by your side and relax your arm - hang loose - then with a long arm bring the bow around from the side to rest your arm weight on the strings through a relaxed bow hold.
Still on basics -
* Slow bows on single notes, varying bow speed, weight and contact point to examine tone and building resonance,
* Note starts and stops in both directions anywhere on the hair,
* Use simple repeated patterns of fingerings in ist.position ,mixed with some bowings, to establish control over rhythmic rise and fall, and timing and coordination,
* Then practice a walking shift ( e.g. last five notes of D scale, 014242410 repeated) polishing your technique as well as timing and coordination.
* now work on two adjacent scales over two octaves with some basic bowings, e.g. E and F, using major, both forms of minor, their arpeggios as well as Dominant and Diminished 7ths. This will cover all the notes over a sizeable distance.
Whatever you do of the above spend at least three minutes on each, covering them all on a fairly regular basis. This should quickly re-establish confidence in your core techniques as well as warm you up, mentally and physically, ready to do some hard work.
Rather than butt your head up against very difficult pieces that were once played with ease, stick to playing medium difficulty stuff really well with lots of expression. I rather like Sturm 110 Studies, Slama 66 Studies in all Keys, and Lee 12 Studies (all IMC publications). There is plenty of time later to take on "Mt. Everests".
You may have to wake up the flexibility and sensitivity of your right wrist hand and fingers. With cupped hand press the end of your curved thumb against the end of your second finger and rotate your hand around your wrist in both directions. Open your hand from a fist to fingers splayed and straight then close, over and over again. Drum your fingers up and down on the table as though you are doing five finger exercises on the piano. With your fingers straight flap them from your big knuckles. Feel both sides of your hand come alive.
If you are still physically stiff there are a range of stretches and exercises that you can do
to loosen up shoulders,arms,wrists and fingers.
I know how you feel - I am going through the same process now that I have moved to a "new" smaller bass.
DP
