"I won't give up..but it's going to wear me out!"
Yeah. Only the chosen few who play them know the stamina it takes to play the bass.

"Am I going to give myself a horrible habit if I sort of clamp the bass with my forearm/elbow until I feel more secure about letting it lean loosely against me?"

In a word, yes. The suggestion above with regard to its being like a dancing partner is pretty descriptive. You may need to adjust the foot (peg) to achieve the height and balance that works for you. I'm hoping that you are standing slightly behind the bass with its upper rear curve nudging your side. The inclination is to want to have a three-point balance scheme. However, it just doesn't work well that way. Your left arm and hand need to work independently of the support and balance issue. In other words, the foot and your side are the only two things that hold the bass in place. Naturally, you'll need to let the foot take most of the "responsibility" for the support.

Try this. Stand the bass on its foot and find the point at which it is most balanced - the point at which you could almost let go and have it stand. Next position yourself slightly behind the bass as I mentioned, but a half of a step away. Then lean the bass into your side.

I don't know if I have described this balancing act as well as it might be, but I hope it is of some use. Finding that balance is somewhat difficult at first, but becomes second nature after a short time.