Shipping Prices with Printful

[srvc]

Hi!  

I have a POD store on Square Online, fulfilled by Printful.com.  Printful has well-defined shipping rates which I'd like to follow as closely as possible.  It is quite a range:  a single t-shirt costs 4.69 to ship, +2.20 for each extra shirt;  meanwhile, a single pint glass costs 10.49 to ship, +4.50 for each extra glass.  

I see that Square allows me to a build Custom profile for any specific item, which seems somewhat helpful (though, why not by item category...).  And Square also allows me to build a profile with per-item shipping costs (e.g., 4.69 for 1 shirt, 6.89 for 2, etc.), but that is only an option in the Default type profile -not in the Custom type of profile.  

I don't want to charge customers 10.49 to ship a single shirt, but I also don't want to charge them 4.69 for a single pint glass -and thus eat the ~6 difference myself.  I'm sure I'm not alone in this boat, so what is everyone else doing?  I'm new to this, so go easy on me  (o; 

Thanks so much, and happy sales!

Chaz