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Live in an old house and have a TP-Link Archer C9 which gives a decent enough 2.4 & 5GHz signal upstairs but not downstairs where the signal is considerably less and even absent in some rooms. I'd like to extend or boost the wifi so what are my options? My requirements would be:
- Fewest number of additional network infrastructure devices (to keep the clutter down).
- Same wifi network downstairs as it is upstairs.
- Some future-proofing, i.e. if I upgrade the C9 in a couple of years (probably staying with TP-Link), something that is likely to still work.

Or am I going about it wrong and should I be upgrading the C9 instead (although I'm aware that 5GHz signals don't do that well with old houses anyway because of thick walls etc.)?

Many thanks for any advice.