If you're on a tighter budget, you might need to make a trade-off and go for some slightly less dense foam. Tim says a density of 1.8lb is acceptable, or 1.5lb at an absolute minimum.
"If you see foam less than 1.5lb I would start to get hesitant. We don't use anything under 1.5lb. You know, if that's what you can afford, and that's your budget, that's okay. But the durability when you get below 1.5lb, in our mind, makes us nervous."
The way a bed is stored plays into it here – if a bed is going to be roll packed for more than a few weeks, 3Z Brands like it to be 1.8lb density, to ensure it springs back into shape correctly.