Mixing Milks

[Natzer]

DD (8 Months) wakes up at about 7am, has about 3or4 oz of milk, then has a nap about an hour or so later, but wants another oz or 2 before going to sleep.

Normally I make up the bottles every evening, cool quickly and then store at the back of the fridge, however I was wasting alot of milk this way and having to make up an extra bottle. Now, we have decided to give her a box of ready made (200ml) so that it is still safe to drink an hour later so that she can finish it off before her nap.

She is on first milk still, but as we know follow on milk is cheaper, can I give her follow on (ready made) milk first thing, and then have first milk for the rest of the day?

cant see why not

my friend does the opposite.... she has moved her DD to follow on milk, but when out and about they use cartons.
Her DD doesnt like / wont drink cartons of follow on milk, (fine with powder) so when out and about they give her cartons of first milk which she will happily drink.

That's interesting that she wont drink cartons of follow on, will buy just one and try her on it first I think to make sure.

I don't want to put her on follow on all the time as she does get constipated.

Yes, that's fine to mix, although if she gets constipated on follow on it may be worth sticking to infant pre-mix as she's probably sensitive to the extra (potentially risky) iron content in follow on.