I made a crawling track for my baby and I think it was a great benefit to her. I am so glad I was able to do it. But putting it together was a bit difficult so I completely understand where you are at.
I have heard of someone who removed a slide from a little toddler play set and used that. I think the problem with the slide though is that it is not soft for the baby, but maybe you could put a narrow mat down the center. I think I also read of someone who did put a play mat on a board and then elevated one side. The board would need to be wider than a regular crawling track so that you are not afraid of the baby falling off the side and you would need close supervision which I am sure you would give your baby anyway. Having the sides to push off does help the baby, especially to go straight, but more than anything I think it is the incline and the assistance that a bit of gravity provides the baby. If you are going to use a mat just look for one that doesn't grip too much as you want the baby to be able to slide.
If you can't do any of that than nothing beats tummy time! Easier said than done,
. Some little ones just don't go for it, so don't be discouraged if that happens to you. Just start off in small doses but with many opportunities throughout the day. You might find it impossible to follow the schedule Doman sets out in his books, but any stimulation you give your baby will benefit him/her? as he himself says.
Good luck!