Depends how important the data is, how long is long term and how budget is budget, but assuming you don’t want to risk losing anything, backup best practice is the 321 rule

3 copies 2 different media 1 off-site

I’d almost always say a cloud provider for your off-site backup, but if you don’t want to do that, it depends how much you want to spend.

There’s no guaranteed do-it-once-and-you’re-done approach here, as all data can degrade. For instance if one of your backup media is hard disks, you’re probably going to want it setup in at least RAID 5 and you want to be on top of swapping out disks when they fail. If you’re thinking of the Blu-ray or tape approach, you’re going to want to periodically check that the media hasn’t degraded. You’ll probably also want to plan to replace the backup media every half decade or so to be extra safe (e.g. BD-Rs have a lifespan of 5-10 years).