Anywhere fleshy is going to be the least painful. It's when you are close to bone where it becomes the most painful. But even so, I wouldn't let pain scare you away from a spot. Sure it might HURT at the time but then you'll have it there, pain free, for the rest of your life.
I don't have any experience with weight loss bothering my tattoos, but my older ones are on the inside of my ankles. Not really much weight changes going on there. The one on my inner forearm is brand new so I have no idea how that'll turn out. Now, again, I don't actually know this but I would imagine that a 25 pound loss would not make any difference in a tattoo's appearance if you wanted to make it your onederland present.
Personally, my favorite locations for tattoos on women are inner forearm, inner bicep (I know you said you didn't like that but outside of bicep and inside are two different stories to me!), side of ribs and front of thighs. Do some googling to see what you find attractive!
I thought about making my newest one a reward for weight loss but I decided that I had already waited long enough to get it. It took me several years from idea to actually getting it done. I didn't want to wait anymore, but that's just me =)