I have received some questions about my cover collection, so here are some tips that I hope might be useful.
The basic idea for me was to have enough space for one cover per each independent country and a few semi-independent countries.
My covers are of very different sizes, so I can not use any of the cover albums that are sold in philatelic stores because only C6 format covers fit into these albums. So, I had to come up with another idea.
I ended up in a solution of office binders containing one stiff office paper (maybe paperboard is the correct English word) for each country. If there is one country per each page, two countries per one paper, the total needed amount of papers is about 100.
The covers can be placed on the pages with the help of photo corners, and the papers can be put inside transparent pockets. All these equipments (binders, photo corners, stiff papers and transparent pockets) are sold in ordinary office supplies and accessories stores.
I have found this solution quite effective, easy to use and dynamic enough for my needs. Take also into consideration that the transparent pockets do protect the covers.