Actually, there's really no where of telling your fat level unless you have the appropriate measurements done with the right tools and by professionals. To be brutally honest, firmness is not a determinant of how fat you are as I've clients with high percentage body fat without the flabbiness. That being said, I'm not suggesting that you are like that too, cos honestly, there's no way to determine unless you've seen professionals, such as the guys at Changi General Hospital.
BTW, weight is definitely by no means a good way of measuring fatness. Weight of your body takes into account not only fat, but muscle mass, bone mass and body fluids. So for a really light person, it might mean that they have very little muscle mass and probably porous bones which leads to future osteoporosis. And it could also mean that they might have a far higher percentage body fat than a heavier person who is physically active and healthy.
If you're thinking of a weighing scale, a normal scale is really good enough. Digital is good for ease of reading, and the decimal points. But really, there's no point splitting hair over decimal points or even a kilo of your weight cos a person's weight can fluctuate by 1-2kg even within a given day.
Good luck!