Truthfully, your computer is very underpowered for a game like Arma. I would consider building a standalone desktop if possible, there are few laptops that are equipped to run Arma, and all of them will cost more than a desktop would to build.
You could easily find some used 5th gen intel setups to piece together, or buy the new 8th gen intel and be good for a minimum of 5 years from now. Arma runs heavily on processor (clock speed more important than cores) and ram. I would want a rig that can push a minimum of 3.5Ghz and optimally about 4Ghz, with no less than 16 gigs of ram.
If you keep it simple, a single 24" 1080p monitor and a modest build should be fairly reasonably priced.