A drystone wall is certainly an option. The stone you have is ideal for building. All it takes is a little preparation and some inexpensive materials and...time. Here are some practices I have used which assisted me:
- know your soil type. Clay will shift in a cold winter or a very cold winter. Sand drains freely but is more likely to washed out
- drystone walls are good up to one meter tall or so. Higher than that takes some practice and preparation. (More deadman retaining stones, more drainage, angling the wall into the soil on the higher area)
- a geotextile fabric or soil separator is essential to keep the soil from washing out from between the stones EDIT: in North America these are sold as "Landscape Fabric" or "Weed Barrier". I find the quality of this type of retail product is insufficient for a long lasting job and suggest you source commercial grade products which will be called "geotextiles".
- drainage pipe on the inside base of the wall is also essential. In North America you can buy four inch diameter drainage pipe with a woven sleeve that does the job nicely. I'm sure similar material is available where you live.
- a list of tools you might need is here
- some alternative ideas are here
I find the best part of using stone for your bed is that are also building a miniature micro climate. Stone will warm faster and retain heat than soil. Plants placed into the wall will grow sooner and, if the correct species are chosen, flower faster
My stone wall is starting to shape up nicely after a few years of stuffing plants into every crack. It has been stable for 5 years with a temperature range of -30 degrees Celsius to + 30 degrees Celsius.