Upgrade router or Buy Mesh

Hi everyone, looking for options and suggestions. Thanks in advance

Our ISP is converge (300 mbps) where their modem/router is connected to my ASUS RT AX55 stationed on the 1st floor (got this like 5 years ago, one antenna is broken but wire is still connected). The coverage was excellent but lately, I’m having a difficult time getting signal outside in front of our house (street level) and inside my room. When i have coverage, it’s mostly buffering, disconnections and other troubles.

Our house is pretty small (around 30-40 sqm but with lots of walls and divisions). I mainly need the excellent coverage within my room which is only on the 1st floor because thats where I study. I also sometimes need/use the coverage outside the street in front of our house.

Devices we mainly use are relatively new and latest of this generation so wifi technology can be a factor and might be beneficial to take advantage of. (1 macbook, 1 windows laptop, 2 ipads, 8 phones and 1 android TV) and of course the usual relatives who would ask for the wifi (approx 5-10 phones). All of these devices are not used simultaneously.

I was thinking of upgrading to a new router entirely or maybe just buy a mesh system and use my AX55 as an AP, not sure though if its a good option as my AX55 might be outdated already. Or Just connect the newly bought mesh directly to the converge’s modem-router?

Budget is around 5-15k php. Other suggestions are very much welcome. Thank you so much.