Anyone have any experience with under the bed restraint systems?

My hubby and I have a bed that has a solid headboard, so there's nowhere to tie anything if we ever wanted to spice things up a little, if you know what I mean. 😉
So I've heard that there are restraints that you can put under your mattress and take out when needed. Do any of you own one/have any advice for me?
On a related note, has anyone tried any of those "sex pillows" (for lack of a better term) that prop you up at a better angle? 
We've tried all our pillows and the angle is fine, but it doesn't support my back properly and it makes my lower back hurt. 
Thanks, ladies! 💕

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