If you can move the router to a more central location that would be ideal and purchase a tri-band router to assist with wifi congestion. I would go mesh AP’s instead of another access point as you can expand your setup later and not have to worry about SSID’s clashing. Realistically, buffering can be many factors and I would do the basics first.
A mesh network will improve your wireless signal, you won’t regret it.
Dont you lose speed with mesh?
I use the TP Link Deco M9 Plus system with 3 access points. I have a 3 story house and my internet connection is in the utility cupboard at the front of the house near the front door. I have a unit in my living room on the ground floor that uses ethernet for the backhaul and another in the master bedroom on the 1st floor also using ethernet for the backhaul. Both of these pump out 500mbs. The unit on the 2nd floor uses WiFi for the backhaul and that delivers a respectable 250mbs. Previously I was lucky to keep a 1 bar connection on the 2nd floor so this was a must for me as I wanted my office and cinema room on that floor, which is almost set up. I’ve been using my office for the past few months but what I do notice occasionally is that my laptop would connect to the access point on the floor below even though I was effectively sat on top of the unit in the office. As my laptop is docked in the office I hardwired the unit to my dock and the issue is resolved although I do see my phone on 2 bars sometimes even though I’m sat in front of the unit. All in all I’m really happy with the system, it improved my coverage ten fold and would definitely recommend the Deco M9.
Try Standard Definition, Switch your feed to a lower quality to see if that allows you to stream better.
Investing in good equipment, whether it be a solid router and modem (or a mesh router) and a decent device with good specs does help tho you can still have service issues. However I think most will find less problems with a decent investment in the above, I use mesh and it’s excellent for me.