Ask HN: Middleground between arduino and raspberry pi?

I was asked by my father who is a doctor, to build a prototype medical device for some idea he had.

I did a lot of toy projects using either the arduino or the raspberry pi.

For this project, I need something low power (will run on battery) that will receive data from a few sensor (so it need GPIO) and display this data on an OLED display (I need to plot a graph and display a few metrics).

I feel like the arduino is a bit too low level, the goal of the project is to focus on the idea my father had, not writing a plot engine in C.

The raspberry pi on the other hand seems way overkill (and uses too much power).

So many boards and solutions have flourished lately, I'm a bit lost. The arduino drama didn't help and I lost trust in everything arduino.

I need:

- As low power as possible

- A few GPIO, 5 are enough

- An easy way to drive something like 2x10cm OLED display

- About 1mb of writable internal storage

- A way to prototype and debug that is easier than having to load the program on the arduino. For this the PI is good because I can just run pi programs on linux.