There have been reams written upon methods of bondage. It's an entire field unto itself, that some people spend a lifetime coming to learn.
There are two key points behind all that knowledge The first is safety, the second is effectiveness. One should always look to those in that order.
Your wants are pretty straightforward. A tight tie that gives you good access for tickling, and that your lee is not stressed by it.
The commercial strap option posted above is a more then workable one, and I'll agree that while the under the mattress sets work, they don't do all that well in limiting as much motion as one would desire, so bind off to the bedposts is the way to go.
But one my not have bedposts. So you may need to go to some simple rope work. I'd suggest some soft cotton rope, not unlike what you might make a clothesline with. It's thick enough to not cut, and soft enough to not mark or abrade.
Check out some online rope work videos that show the basic tie (loop, ends through loop, tighten around what you are tying, wrap each limb, synch in center and tie off in center, so the knot is not on a limb, but between them) and then use a linear bondage. Lee lays arms above head, legs together. do ties ate wrists, above the elbows, above the knees, ankles. Now you can tie down the wrists to any anchor point you have (usually a bed leg) and the ankles also (opposing corner bed leg) and tighten as much as you want, and the lee can comfortable take. Now you have access to the lee from hands to feet, and they are not mobile at all.
https://www.ropeconnections.com/my-favorite-way-of-tying-wrists/
Here is a nice instruction on the tie.
Of course with the bed legs you can do the traditional 4-point spread eagle also, as tight as needed.
Just practice a bit with a willing partner and you'll get good at it rather fast.
Myriads