There are several methods and I’d recommend a combination.
For your home internet, use only ethernet cables to connect to the internet.
You can start by getting into your router and switching off the wifi setting and having your internet run through cable.
Use TP-Link or similar. TP-Link Adaptors do the job fine.
For walls there are two basic options, materials for walls and other large surfaces and areas or YShield paint.
A range of wall and surface covering products are available at Electro Smog Shielding
According to the manufacturer, YShield screening paint stops over 99.9% of incoming radiation across all mobile phone frequencies, TETRA, 2G, 3G, LTE (4G), WiFi and WiMax. Apply as you would any paint using a brush or roller. Yshield is water based and can be used inside the house, on walls, ceilings and floors, or on outside walls. One coat covers about 7 square metres per litre.