I do prefer thicker mat because of the layering, its more comfortable. Both are fine but it’s up to you. Good luck.

Either either I suppose I tried the may personally though whatever works for you

Either works fine. Always remember to supervise!

We had two mats for our little one, one with pictures, textures and playthings attached to the mat, and the other with an arch of toys and rattles hanging off for him to reach/look up. I would often prop up a black and white book to point and read to him, or place a mirror in front of his face. Its not so much the mat or blanket but how we could make it interesting for him as he hated tummy time and stretching his time was difficult!

I started with a bed to make them comfortable then a playmat

Yes I’d say either blanket or mat. Wouldn’t matter too much which one. So long as you don’t use a really fluffy or pully type blanket for a very young bub where pulling the material may be a choke hazard or breathing hazard.
And remember that tummy time isn’t just bub on the floor – can be bub on your chest encourage to look up, bub on you or on a solid bed with a towel under (supervised obviously) or even bub up on your shoulder high and using their neck and back muscles. Not all bubs like floor tummy time. Lots of other ways to get tummy time too.

Either will work, just make sure to have plenty of toys to keep them happy and amused, and only for short periods at a time