Any *box* that will fit inside the flat rate bubble/padded envelope will be fine, of course. If you learn how to package items the FOMO way, however, you will find you can ship even larger items than otherwise. What I mean is that if the larger item were boxed first, the square corners of that box would then cause it to be too large to fit inside the envelope, but with FOMO packaging, it can still fit. Yay! (Those pointed corners sticking out account for taking up a lot of room inside the envelope.)
The nice thing about this for your sales is that because shipping can be a smidge less costly for certain merchandise (that this will be sized OK for) it allows you to be able to offer it for a bit less to your buyers. That lower cost makes your offerings a bit more attractive to many buyers, and that will bring you in a few extra sales that you might not otherwise get. But you will still be able to pocket the same profit and sometimes even more, than the sellers who have to charge more for shipping because they don't know how to ship using the less expensive envelope method.
