Dakotamaid is totally right!!
Tape a toothpick on each END of your dining room table in the middle of the width of the table (to mark the middle point).
Fold your backing in half to find the middle and position it precisely onto the toothpick. Match the middle of the quilt back (at both ends of the backing fabric) to the toothpick. Put the right side down, of course.
Let extra fabric fall on either side of the table.
Now put your batting onto it.
Now put your quilt top onto it. Match the middle to the toothpick.
Each time, for each layer, make sure the middle is matched to the toothpick for each layer.
Smooth out, pin with lots of safety pins, or baste with extra large stitches. Move from the center to the sides. It's very easy.
You have sandwiched your quilt -- ready for quilting it!!

I use the livingroom floor as a "design floor". It has carpeting, so a bit easier on the knees. However, when I sandwich, I use the tile floor in the greatroom because it is a large space and I can tape the backing to the tile to ensure it is smooth. Depending on the size of the quilt, I sometimes need to continue to lay it on the tile and re-smooth between quilting sessions. I use the kitchen island for smaller quilts. I am approaching 50 and so far have had not had problems with knees and getting up and down from the floor, but I imagine those days will come soon enough!

I'm lucky to have a longarm....no basting, layering or pinning required.

I know some older ladies who get the long arm quilters to baste their quilts together. Then they take it from there.

i do the same the floor and my knees do not like each other!!!!

Same just a table and work out

I go down to the library and use their auditorium. Just have to call ahead to see if it is booked for the day. Its free to use the room. Large tables sure make it easy to pin baste the quilts.
In summer time, I have 4 saw horses and lay a sheet of plywood on top, then do spray basting on it. Do this on a day there is no wind as I set it up in the back yard. I don't spray baste at the library because I am afraid it will over spray and get on the table or floor.

MarySews,
I do understand. Even though I am not quite 50, I cannot crawl around on the floor-surgeries on feet and ankles. So, what I recommend is what you are doing now, with a twist.

What I do is slide the board under-then use clamps (you can get them from any hardware or walmart) with the rubber ends-three sides to get some tension. Then start basting.

Hope this helps.

We live in a motorhome FT. Barely room for sewing machine. I use the big tables in the community center to sandwich my quilts.

I just read that someone uses a clothes line...this is a wonderful idea. I will try that next time...and do it outside. Now I just need a clothes line...project for the hubby....