As much as you'll hate to hear it... but if you have to replace your motherboard to upgrade the CPU, you're better off just buying a new system altogether for the sake of simplicity.
Because, if you have to replace the motherboard, you'll need to replace the CPU & the RAM (to accommodate the new motherboard, which would likely perform better), then potentially the graphics card (although this isn't as big of an issue nowadays with standardized connections). While you wouldn't have replace your storage drives, the upgrades costs have a high tendency to snowball out of anticipated control.
It's because of that snowball effect that makes it more reasonable to buy a new system instead of attempting to upgrade ONLY the CPU.
I know it's not the answer you want to hear, but it's the harsh truth that you'll have to deal with & will likely be a similar story when you visit computer repair / build shop.