How do you make a t-shirt bigger?

[FabMarta]

Happy St. Patricks Day, everyone!
I bought a Mamma Mia t-shirt online that was "one size fits all".  (Hah!)  I think it was meant to be a misses t-shirt, and I am about a size 14.  So, if I don't want everybody seeing my business, I'll need to recon this t-shirt.
It's black, with rhinestone type studs on the front saying MAMMA MIA!
There are lots of instructions on how to make a shirt smaller, but I'm wondering if anyone has done this, and if you have any suggestions, tutorials, or the like.
I can't wait to hear what your ideas are.
Thanks for your help!
Fab Marta

[Aislynn]

Unless it's got a good seam allowance to it, the only way I can think of to make a shirt larger is to either add fabric (preferrably in an inconspicuous place, like in the side seams), or to slice up the back and add grommets and close it with lacing, corset-style, or some other sort of system that would leave part of your back bare.  Is it tight all the way around, or just in certain areas?  If it were just snug across the chest, I'd consider cutting a slit in the back, partway down, finishing both sides, and add ties to the top, creating a keyhole sort of a thing.  Hope this helps!

[FabMarta]

It is too small in the chest (Thank you very much, post baby boobs...) but it is too small everywhere else too.
I'm pretty well proportioned, it's just like a VERY snug babydoll tee.
It's black- would there be some way to add fabric to give it the look of a layered Tee?
I'm not quite svelt enough for open back/ lacing.
Thanks for the idea, though!  This is exactly what I'm looking for!
Has anyone done a recon into a layered type T?
Fab Marta

[pandamae]

sew in some side panels or a panel under the bust in cutesy fabric or add some fabric to the bottome to make it longer?