Ooh, it's so much fun to plan new bags!! Keep in mind that there is a first time tpf discount, in case you fall for a leather not included in the sale.
I have tinted chocolate. Omg, I love it! It's smooth and soft with a bit of a shine to it. I hauled it around Spain and even India, and it seems to have held up well....I have it in a Chiara. The leather is not strokable so much as pinchable and squeezable. Very comfortable to wear in a messenger strap. Comfy to wear on a long aggravating trip or when you get sick while traveling.
I agree that mini-Sofia will not hold a whole LOT of extra items. I love mine, but don't have to carry diapers!! I would recommend the midi Sofia or the mini Ormala....although No cute can speak to the regular size Ormala for that, obviuosly.
The Ormala style can be a bit dressy (black nappa, for instance), or more casual. I think a tinted leather in the mini Ormala would make it as floppy and squshy as my Chiara. (the chiara has a zipper, though).
I don't have the mini Chiara (yet!) but I imagine it would be better than the mini-S for the diaper bag? I think it is a good possibility, and Ignacio can always help you with your decision!!!!
Welcome to Ignes!!!!