I recommend you buy Tuffie fins in yellow. These fins are made of tough plastic and will last a lifetime. They are short enough to fit in a carry-on bag so they can travel with you anywhere. High visibility yellow helps your buddy see you in our sometimes murky conditions.
Even if you order a pair of long carbon fins later, you will never regret owning these. Don't worry that they are plastic - your fins will never be the thing holding back your freediving (at least until you start breaking national records!). I have worn these in competition and my instructor trainer, world class freediver Johnny Sunnex, can dive deeper than 80m in these. They are powerful enough.