For height, look at the part where the fingerboard meets the headstock, and set that at eye-level or slightly above -- well, at that level when the bass is slanted into playing position.

Half the battle on bass is strength, and that does not come overnight. The Simandl method (as recommended by Mitch) provides ways with dealing with the issue. One principle is that whenever possible, keep the fingers that arent playing the note ("behind" the fretted note) pressing down the string. E.g., when you are fretting a note w/ the pinky/4th finger, ALL the other fingers are also holding the string down. Third/ring finger is not used to fret notes in the lower reaches. 1st, 2nd, and 4th are splayed out, for reach and strength...so within one hand "position", you reach 3 notes on a string, not 4 (i.e. unlike guitar).

The positions are very important, too, in reaching the right notes in tune. Don't learn the instrument note by note by fishing. Instead, maintain a hand position as a bloc that moves in synch up and down the fingerboard.

When standing, let the corner of the bass fall slightly into your left-side crotch, with your left foot partly extended.No reach around from behind :~) The goal is to get the bass to stay there without holding onto it with your hands -- you shouldn't be trying to hold up the bass with your hands and play at the same time.