Logitech keyboards and mouse are the big wins....they last long for years if you keep them in good condition and actually clean between the crevices. I've had mine for years and they still work
As for your question, is your keyboard and mouse running by cables or USB plugin?
Because if keyboard/mouse are running by cables, you can easily buy a extension cord for keyboards and mouse but I would make sure it will fit the jack or not. I wouldn't want you to buy that doesn't fit into your pc.
If its running by USB...there is a lot of USB keyboard you can use but if you're asking for extension...I believe you should buy a USB port connector.
For example: USB port connector will be connected directly to your computer then the keyboard/mouse will be connected through the USB port connector. It will most definitely give you a longer extension. Hopefully you understand what I mean.