The way I see the general situation… assuming this is that “can’t afford to lose” kind of data, which seems to be the case, I would just make say two copies on to quality DVD recordable media (Verbatim and Taiyo Yuden) as those should last for the foreseeable future as I have some over 10 years old and they still scan well which means they will likely last for the foreseeable future. I would guess an easy 10-20+ years minimum unless disc degradation can accelerate out of no where but even if that happens, being I got a copy on a different brand I would have to think the odds are in my favor that they both won’t fail at the same time and you can just occasionally run a disc quality check on those once every 5-10 years or so.
but with that said… even assuming the DVD etc discs last for a lifetime, will DVD etc drives still be around in 10-20+ years? ; because I would imagine it won’t be hard to find them for another 10 years or so, given they are still being sold, but beyond that, who knows. which is why I think, at least for the most part, your better off using hard drives as it’s more practical/cost effective to just make multiple copies across different hard drives and store them externally and accessing that data will be MUCH faster and MUCH more convenient. you can even use something like RekSFV ( http://www.kifoth.de/jane/misc/#RekSFV ), or another SFV program of your choice, to check the integrity of your data as you can simply make a .sfv file on your known working data and then use that .sfv file (you could always back these small files up to Google Drive or the like) and it will check your data so you won’t have to worry about your data getting corrupted without you being able to run a fairly quick check on it with the .sfv file.
with that said… I am not sure if BD media is as reliable as DVD media which seems to be more proven. but I am sure there are others around here who are more up to date on BD recordable media than I am as I never followed it much simply because years ago hard drives became cheaper than using recordable DVD media and are all around better in general (although recordable media has it’s advantages like you don’t have to worry about accidental data deletion etc) as about the only time I still use recordable DVD media is for family photo/video backup as I have a copy or copies on at least a couple of different hard drives along with the DVD recordable stuff and some of it backed up online using those free sites which offer 50GB of storage etc. I am not relying on those free online storage backup places though but it’s more of a okay-ish backup in case of a house fire or something like that. also, if you use online backup… if you don’t want anyone potentially seeing your uploaded data then it’s best to encrypt it(there are free programs online like VeraCrypt or 7-zip etc) and then store your super secure password (you can use a password manager to generate a secure password for use on this stuff) in a different location etc.
also, to be extra safe you would have to account for potential house fire… in which case online storage would be a possible option, which appears you already did this, or keep additional hard drives at another persons house you know/trust as the odds of both your house and theirs going down at the same time are very slim. while online storage is a nice option, I personally prefer to have physical copies over online storage in general.
I would say what I mentioned above pretty much sums up your options as I can’t imagine their being much alternatives to that.
sadly, a lot of people don’t even take basic measures to protect their super important data as they will just have the only copy on their computer (or smart phone etc) and when that dies on them, reality sits in that it’s all gone. many seem to have to learn the hard way as I figure having two copies minimum on two different devices (be it two hard drives or recordable media etc) should be a bare minimum even for people who are lazy as while you could get nailed with virus (say ransomware etc) at least you got reasonable protection against hardware failures. while you could do the two copies thing on two internal hard drives it would be safer to have one copy on your main device and then another copy externally as this is probably one of the easiest things to do and should give one decent protection from data loss with minimal effort.