LOW B/C EXTENSION

[bigmatteo]

hi to all ,
i want discover how to use low C/B extension , theese are my questions :

playing in stand up position the nut is at my eye level again ?

if i need to make a C , C sharp , D chromatism were i take my thumb ?

if i need to make a D sharp , E , F chromatism were i take my thumb ?

there are some feature to see wen i choose an extension ???

i play both jazz an classic music i am also a five string Double bass fun but at the moment is too expensive for me so an extesion woul be right thing !!!!

many tanks in advance matteo