Question about iron/no-iron formula (first time mom)

I plan to breastfeed and pump for 70-90% of my baby’s meals for at least 6 months but I’d like to have some formula on hand in the pantry for the occasional times we may need to supplement her feedings (like if I have a low milk production day or my husband or mom/MIL is/are watching baby and run out of my pumped milk).

My mom has adamantly told me that formula with iron causes constipation for baby, sometimes severe, and that I should look for formula without iron.

I am not really finding any without Iron?

I’ve just begun looking into this, but I thought asking here would be worthwhile as my mom’s experience with raising me (32 years ago, and I was strictly formula-fed) is obviously a bit out of date.

The articles I’ve pulled up all stress that babies who are not breast fed really need iron. I’m sure that’s true, but I plan to breastfeed and basically just use formula as a backup..... but if we’re using it only as a backup, maybe the constipation issue would be a non-issue?

Thoughts? Advice?

(Also no judgement about people who choose to do one way or the other or a combo! I am blessedly in a position to work part-time from home so this feels right for my family but everyone is different).

Thanks moms!