Advice on Health Insurance (Brussels)

I am a Bulgarian national, retired from the diplomatic service some time ago.For various reasons I intend to relocate to Brussels in a few months. The net search for a suitable health insurance has produced rather contradictory results, so any advice from old hands would be welcome. Also, what exactly are the official steps for registering as an expat in Belgium? I must underline that I have a decent income an will NOT approach the local social services for assistance or look for employment.
Thanks in advance.