i don't understand about technology

Internets! I am thinking about buying myself a smartphone, since my current phone is getting somewhat elderly. Do any of you have any advice for me at this momentous time in my life? I am having some difficulties as I have never actually chosen myself a phone before in my life: my parents got me my first one, lo these many years ago, and the two I've had since have been my sister's cast offs. I am v. torn between going for something super-basic or just biting the bullet and getting an iphone - on the one hand, iphone = extra monies, but on the other, the airtime cost seems to be the same... Thoughts?

The major hurdle is the cost - I currently have a pay-as-you-go phone which I put money on every couple of years at most, so whatever I pick is obv going to be a major jump price wise, thus any advice on minimising this v. gratefully received! Specifically if anyone knows a way that I can get a plan that brings the cost down by giving me hardly any minutes, and not THAT many texts*, but still gives me a reasonable amount of data (...what even is a reasonable amount of data?), that would be awesome.

*I remember the days when you just bought a bolt on that gave you a maximum of five hundred free texts a year, limited to five per day, and this seemed like joyous bounty except on days when you were trying to organise group events and had to find other people to split the texting with. *nostalgic sigh*