When to upgrade RAM based on free output

I have a java application that runs on a Linux server with physical memory(RAM) allocated as 12GB where I would see the normal utilization over a period of time as below.

sys> free -h
              total        used        free      shared  buff/cache   available
Mem:            11G        7.8G        1.6G        9.0M        2.2G        3.5G
Swap:            0B          0B          0B

Recently on increasing the load of the application, I could see the RAM utilization is almost full, and available space is very less where I could face some slowness but still application continues to work fine.

sys> free -h
              total        used        free      shared  buff/cache   available
Mem:            11G         11G        134M         17M        411M        240M
Swap:            0B          0B          0B
sys> free -h
              total        used        free      shared  buff/cache   available
Mem:            11G         11G        145M         25M        373M        204M
Swap:            0B          0B          0B

I referred to https://www.linuxatemyram.com/ where it suggested the below point. **Warning signs** of a genuine low memory situation that you may want to look into: - available memory (or "free + buffers/cache") is close to zero - swap used increases or fluctuates. - dmesg | grep oom-killer shows the OutOfMemory-killer at work From the above points, I don't see any OOM issue at the application level and the swap was also disabled. so neglecting the two points. One point which troubles me was available memory is less than zero where I need a clarification **Questions:** In case available is close to 0, will it end up in a System crash? Does it mean I need to upgrade the RAM when available memory goes less? On what basis the RAM memory should be allocated/increased? Do we have any official recommendations/guidelines that need to follow for RAM memory allocation?