1 more and next door neighbours

We have been exploring adding 1 more to a Numicon plate. We noticed that the numbers became a bit bigger. On a number line, the numbers were next to each other and we said they were next door neighbours. Some of us knew straightaway what 1 more would be and some of us counted the plates to find the total. Some of us had to work out what my number was by listening to a clue.

1 more than 5 is 6.
8 add 1 more at the top is 9
When I add 1 to my number, I make 4. What is my number?