If the router is directly below you, what is stopping you from dropping an ethernet cable through the floor and down the wall of the other room to the router? If that's not an option, then like Bill said, maybe try WiFi 6e, but the cost of that is not going to be small for a new router and wireless adapter. Powerline adapter might just be your best bet, but that too isn't going to be as cheap as an adapter only solution would be, but since that won't get you the results you're looking for you may just have to accept that anything which will get you near where you want to be is simply going to cost more than you had planned.