Probably the best idea would be to get in touch with a local dive club. I am not sure where exactly are you based in Belgium, but there is big possibility that you have a dive club in the area.
As someone mentioned earlier, a dive club in Europe will be working under CMAS diving association, which is a club orientated association with a bit longer course duration and slightly different ("old school) approach comparing to other associations such as PADI, SSI, SDI etc..
Longer course duration has a lot to do with club members having their lives, their work and other activities, and come to a diving club once or twice a week for example, so an OW Course would usually take all winter with continuing education during summer, compering to doing a course in a tropical diving center that work under associations such as PADI, SSI, SDI, NAUI,..where people come to during their holidays and have only 3-5 days to complete the course.
If you would like to dive all year round, during the week, after work, on weekends, etc. then being part of a local dive club is very good option. You have yearly fee to pay and you dive for free or with small symbolic addition charge for each dive. Courses are much cheeper too compering to prices in dive centers.
Regarding online courses, most associations these days have e-learning programs, for most of the courses out there. E-learning courses you can purchase on association websites (for example tdi/sdi website). But bear in mind e-learning is only giving you theoretical knowledge and after complication you will still have to do practical part of the course in order to be certified. But if you are into theoretical knowledge you can go through as much e-learning as you want, without enrolling into and paying for the full course. After completing e-learning program for particular course you will receive e-learning diploma which will be valid later when you want to do practical part of courses, provided you are going to do it with same association.
As for overweighting and being on the knees. Instructors overweight their students and place them on their knees because like that is easier for instructor to keep everybody under control. If all of the students were perfectly weighted it would be much more work for instructor who is probably on the limit with student to instructor ratio on that particular dive, which could be only a first of 3 dives for that instructor on that particular day. Working for super busy dive centers instructor unfortunately have no options and do not make any decisions.
I do not saying teaching buoyancy while being on the knees is the right way of doing it, absolutely not and me personally I do not teach that way, but I am just trying to explain why is that and how it works in reality.
Me personally I only tech one on one, or smaller groups, max 3-4 student divers per dive, depending on the course too. That way I can concentrate on all students and do it properly.
In the end, the instructor is the most important part of your education, it doesn't matter to what standards he is going to be teaching to, because anyway all the associations have to comply to a same standards made by WRSTC.
It is difficult for you to know which instructor is good, I agree, but checking with someone that already did the course with that instructor will give you pretty good insight.
I hope this helps