E. Pluribus Unum's link about setting up a network ten years ago...A little late to the party, I just want to reinforce that this ten year old link is 100% relevant and correct a decade later! You do not need to spend a lot of money or install software to solve this problem. It's actually defined as part of the wifi standard: you can have the same network name and password set up on multiple routers around your house.
If you have old routers lying around, this is a great way to utilize them. Make sure you understand what you are doing, though! Turning on a bunch of new wireless stuff might blow up the carefully set up wireless environment installed by your kids, etc. 😅
Old hardware can sometimes find new life with open source software. The dd-wrt project has been writing a router operating system for almost twenty years, that can be used to turn your old routers into repeaters with ease.
I have been doing this kind of stuff for a long time, happy to answer questions.