OP, my DS is the same age as yours and until 2 months ago had half a dozen spoken words. He's now speaking in sentences. So the first thing to say is that some children really are "just" late talkers and catch up fast once they find their words - so stay positive! However, it's impossible to tell for sure which children will catch up without help and which would benefit from early intervention, which I think makes early intervention important for all.
I really recommend checking whether you can self refer to SLT services in your area. Round here, the HVs guidelines and practice are to refer children a year later than the SLT's own guidelines suggest - why, is a mystery to me but we duly self-referred DS to SLT, and he was assessed and offered 1-2-1 SLT. You can generally phone or download referral forms online. The wait fir an assessment can be several months or more (16 weeks here) with a similar wait for any follow-up or therapy.
I also highly recommend the Hanen book "It Takes Two to Talk". SLT at this age will be more about supporting you and anyone else who cares for DS to communicate with him in ways which will best help him - and giving you confidence that you're doing your best for him. This book is a great resource for learning techniques to help, if private SLT is out of the question.
It's counterintuitive but regarding "encouraging" him to speak, don't push him to talk - observe, wait, listen (OWL), create opportunities and model what he might say but avoid pressure.
Makaton or other supported signing is also worth looking into. It really helped our son, and was advocated by every SLT (NHS and independent) for speech delayed toddlers. It's not just that it's a means to communicate basic needs and ease the frustration, it also helps with getting the idea of back and forth interaction/conversation, which is a basic building block for speech.