You want Boas to be lean and muscular.
https://ball-pythons.net/forums/show...72#post2657072
Look at the pictures of Behira on this page of her thread. You can see her spine too, but it's not protruding. It doesn't look like Sin's is either.
Having said that, 11G's, or any hopper, is probably a little small.
I would bump up to weaned/small mice (14-19G). The meal should leave small lump and be gone within 48 hours (completely gone/unnoticeable). If the lump seems a little larger than normal, feed 10-14 days later instead. Boas have very slow metabolisms. As you can see, even though, at 179G, Sin's meal size has been on the small size, she's still growing and looks good.
Remember, with boas, better to feed smaller than larger, when in doubt. Big meals can be bad for them, especially if fed too soon after.
At 250G+, you can feed regular/adult mice.
Over 350-400G, I would start offering weaned rats. Over 500-600G, I would start offering small rats, but at that point, you should be feeding ever OTHER week.
Don't hesitate to keep asking questions. Also, feel free to PM anytime. I've learned a lot keeping, now, 2 boas, both from a lot of research, some trial and error, and from some good peeps on here.