My opinion - I think it really depends on what you need and what growth looks like.
I would personally put the data and log files on different disks if you need fastest performance from the database. But with those fast disks, you probably won't notice much of an improvement by having the data and log on different physical disks unless you have a lot of write operations. But with the database being relatively small (55 GB) and the smallest set of disks in your list being 960GB, you may want to refactor some of those things around. With options 2 and 3 you have a LOT of disk for that small of a database and option 1 is a HUGE disk for such a small database.
Things to note with all 3 options - you have a max memory of 128 GB. With your current SQL RAM usage around 50-60 GB, what is your "MAX MEMORY" set to? If it is set to around 60 GB currently, that would explain why you never use it all up.
I would be looking at what you are wanting on that system and what you plan to use it for going forward. Having SO much extra disk while having only a little spare RAM in options 2 and 3 doesn't give you much room to grow into that system before you will need to buy more hardware (RAM).
My recommendation would be to use a modified version of number 2 - I would shrink the disk sizes down a bit in order to get more RAM. If I am "Upgrading" my system, I am not going to reduce RAM to what I see as the "bare minimum" (SQL + 4 GB for OS). I would keep the 128 GB of RAM and investigate how SQL is configured because it could easily be that you would benefit from the full 128 GB if it was configured differently. Even if it is configured to use 2 TB (I hope not) and it is only using 60 GB out of the 128 GB, I would want room to grow. If the utilization of the server increases over time, I want to make sure I have room for that growth.
Same thing with the disk within reason. I want room to grow, but having nearly 1.5 TB of disk with option 2 for a 55 GB database plus OS, which would probably total around 110 GB used, seems like overkill. BUT I also don't know how quickly you filled up that 55 GB in your database. If you are adding 55 GB per month, 1.5 TB of disk will only last about 27 months (roughly). But if that is 55 GB per year, then 1.5 TB of disk should last about 27 years; assuming linear growth. In 27 years, you are likely to upgrade the system multiple times and as such probably don't need to have 1.5 TB of disk.
On top of the RAM recommendation, you may benefit from in-memory tables, which would use more RAM. You might not; it really depends on how you are using the database, but in memory tables can offer some performance boosts while eating up more memory. Since you have the memory available, might as well use it. Mind you, I don't remember offhand if 2012 supports in-memory tables; MIGHT need to upgrade to 2017 or higher for those.
The above is all just my opinion on what you should do.
As with all advice you find on a random internet forum - you shouldn't blindly follow it. Always test on a test server to see if there is negative side effects before making changes to live!