How do I reduce my MIDI latency without ASIO4ALL?

So I just started getting back into music production and I remember that I always used ASIO4ALL when I wanted to record something from my MIDI keyboard. Now many of you might know that using this driver disables sound everywhere except for REAPER itself. Now I really need to be able to simultaneously listen to stuff outside of REAPER and record MIDI from my keyboard at the same time. I just can't wrap my head around this whole ASIO, audio interface and driver stuff, so I have one simple question: What do I need to buy to get the input lag from my keyboard to ASIO4ALL levels while still being able to have sound in every other program? I guess I need some audio interface with MIDI input for this that also acts as a sound card, right? What I can't do is buy a new internal sound card since there's no more space in my PC casing because the GPU takes up all of the PCI-slots. So I think I'm looking for an external solution via USB or however stuff like this works. I hope there's a solution for this. I never gave the whole hardware aspect of music production much thought, so I don't really know much about this at all. Thanks!

Try WASAPI. It works really well (Win 10 x64).

Having looked into this a few years ago, midi latency will be at its lowest when your midi keyboard controller is connected directly to a rear-usb port on your PC, bypassing your interface.

Interface 

It's very easy and cheap to get a Two input audio interface that has midi input and output. My alesis io2 cost $75, works great. Sorry to be so vague but there are many, many choices in the hundred dollar range...welcome

Thank you for the answers. I'll check them out, but for now WASAPI seems to indeed to the job just fine.

I use "Direct Sound" (Win 7 64 bit) and it works whenever I have only a Laptop.