We have the Baby Bjorn potty chair.
Here is a link:
http://www.amazon.com/Baby-Bjorn-Large-Potty-Chair/dp/B00...
You can take it to any room and use it, putting it near your child. They don't need a step stool for it. They just sit on it.
Both my kids, have potty trained using this. And they also then went on the toilet with a toilet seat ring, as they progressed.
Right now, your son is still learning, and they may not be able to "hold" it, until the bathroom is available. So, in the meantime, a potty chair is really useful.
Also, as he progresses in potty training, in time, he will on his own, start to tell you when he has to pee/poop. Just not yet. Potty training occurs in stages and is a process. It also has to do with the myelin development of the nerves.
Keep in mind, that dryness during night-time and naps, will not or may not occur yet. Night-time dryness... can even take until 7 years old, which is normal. And accidents may still occur. And per our Pediatrician.
One step at a time.
For night-time... once he is at that stage, a waterproof bed-pad is very good to have... put it right under him, and it makes clean up much easier. I have about 4 that I change out and launder as needed, if my kids wet the bed at night or during naps.
Also useful, is a car potty. For times you are in a car and there is no bathroom in sight or the child cannot hold it or wait until you reach your destination. On www.amazon.com just put in the search words "on the go potty". The car potty, has been a literal life saver for us and our kids. Our friends have these car potty's too. Very useful.
Potty training is in 3-4 stages:
1) daytime peeing "mastery" and in the toilet, being able to tell you and pull down their own pants.
2) pooping in toilet and mastery of it.
3) night-time/nap time dryness.
Also, their ability to "hold" it until they reach the bathroom and them telling you before they have to go pee/poop. AND their gradual ability to actually wipe themselves... which will take until he gets older.
Well sorry for rambling and the extra suggestions.
But the baby bjorn potty chair is really great.
All the best,
Susan