Subs in a basement on a cement floor have a tough time shaking a couch 10 feet away (Ask me how I know). Nearfield is a good option, but that means placing them right behind the couch. Another good option is building the speakers where you have the space 10 ft away and then building a BOSS
platform for your listening position. This will help you get the tactile response.
Even if you don't really have a budget, one should be specified. The DIY forum could spend 3 grand of your money and not blink an eye. If this is acceptable for you, it should at least be stated. The DIY forum tends to over-do things because "If something is worth doing, it's worth overdoing."
Another piece of useful information would be the amount of space in cubic feet available to you for boxes. The lower you want your sub to play, the larger the box you need to build. Once we narrow down the driver and box size, then we can help you start designing the box. The common solution is to just build a devastator. I have a couple and they are great. They are also large and can be expensive if you get the high end drivers at $600-750 each for a 21" driver. A quick peruse of the Devastator index
will give you an idea of what is available for 15-21" drivers and their box sizes. We can also do a simple custom ported design but need to know the driver and box size for that. The Marty Sub
is a good example of that. Additionally, you will need to pick up either an inuke with DSP or a MiniDSP because all ported sub boxes will need a High Pass Filter to protect the driver. And while you're at it, a measurement mic is a helpful tool too. The MiniDSP HD can be purchased at parts-express. For a mic, I recommend the UMIK-1 from Coss Spectrum labs. It is individually calibrated and worth the small premium.
You will have a blast learning and building your own driver. It a great rabbit hole that will lead to years of fun and experimentation.