What make and model of extenders do you have. Thes are always the least satisfactory way (albeit cheapest) of solving wifi connection issues.
To address the wifi issues, VM now supply “wifi Pods” (no longer doing cheap and cheerless and poor value “boosters”). However, their Pods are only free to customers on the 1GB, Volt (or old Ultimate Oomph) packages - is that you? If so they are worth trying - they should work for you. VM Wifi is now “guaranteed” to 30 Mbps/room it’s now called… Wifi Max
See if anything in here helps….
https://www.virginmedia.com/wifi-max
But... If you do want to invest in better equipment, you would need to get either a… (1) Mesh System, (2) Wireless router, (3) Wireless access point(s), (4) a pair of good quality Wifi Powerline Adaptors, or a combination of (2&3).
£100-150 should sort it for most customers with an average property and usage. Spend more for additional advanced“features” - if required.