How to properly use STM32 flash memory as an EEPROM?
Yes, as you've already discovered, you can't erase less than one page at a time.
However, if your parameters take up much less than the size of a page, you could consider creating a scheme where instead of writing to the same address every time and erasing in between each write, you write to a different address within the page at each write. Only erase the page when its full.
So when you want to read your parameters, start reading at the beginning of the page, and continue reading until you get to a parameter bock full of 0xff entries.  You'll then know that the previous block was the last one you wrote.  

There are certainly many other ways to do this kind of thing, for example you could use a bit-field at the start of the page to indicate which blocks within the page have been written instead of having to potentially scan through the whole page. But this may depend on hardware support. Some micros - like the STM32L0, won't let you write anything other than 0x0000 to a flash location if it's not currently fully  erased to 0xffff, preventing you from using it as a bit- field and clearing 1 bit at a time.