They are not your only options if you are in the UK.
Your DS would, in my view, benefit from a Statement of Educational Needs. These are being phased out and replaced by Education, Health and Care Plans, but the process is very similar.
It's a 6 month process, to assess your DS and see what his educational needs are, how they are best met, what provision he needs and where his education should take place.
To get one, you'd need to apply to your Local Authority's SEN Officer. They would then gather some evidence, and make a decision as to whether they will assess your DS.
IF you choose to take this route, you must do it very, very, soon. This is because even if you apply today, you wouldn't get a finished plan/statement until 5th August and your DS is due to start school in September.
He could thrive at a Speech and Language Unit. He could thrive at a Mainstream School with support. It may be that he needs someone to teach him Makaton and use it consistently. It may be that he'll be best served by PECS (Picture Exchange Communication System). Someone, somewhere needs to give your boy a way to communicate beyond simply pointing and crying when someone doesn't understand him.
An extra year at Nursery is not appropriate, in my view - if his understanding is typical of his age, why should he be held back simply because he can't express himself?
It may be that he is just 'delayed' and will develop speech soon. But what would their plan be if he got to the end of next year and he didn't have speech - keep him back for another year???
You need to ask some awkward questions and push for some proper support. Just because he isn't behaviourally challenging, doesn't mean his needs should go ignored.
Just to give you an idea of how the system can work, if the child is causing them a problem:
My DD1 attended preschool at 2years 6months. By 2years 9months (with the 6week summer holiday in between!), the preschool asked to have someone 'observe her' so that she could 'have some extra attention.' The same day as the lady observed her, DD1 was given complete 1:1 support.
She had a full statement in place by 4years 1month old, and a special school place was given without a murmur.
The reason? Well the official line is that if a child has additional needs they must be identified and met. The real reason, IMO, is that DD1 was a problem for the preschool staff. She was willful, full of energy, no sense of danger and no understanding of discipline boundaries. She did what she wanted when she wanted to and there was nothing anyone could do to change it. I am almost certain that if she had been of a more passive personality, then she would have been sent to mainstream until the difference between her and her peers was so great in year 3, that she was sent to the wonderful special school she's been at since year R.