Whilst Namibia does have a huge coastline with the Atlantic Ocean, the coast is unsuitable for a beach holiday.
The cold currents which make the waters rich in sea life, do not make for pleasant or safe swimming, and regularly create heavy and cold coastal fog. Flying along the Skeleton Coast, or visiting Swakopmund and Walvis Bay area for a few days is highly recommended as part of your holiday, and you can choose to give yourself a few extra days to relax in these destinations if you prefer. But we would not recommend treating them as potential ‘beach destinations’.
If you are just looking for a little relaxation within your Namibia itinerary, there are places where this can easily be included. Most notably there are luxury lodges in the Namib Desert where you can include extended stays in order to allow time to relax, read book and lie by a pool. Alternatively, you could begin or end your holiday with a few nights near Victoria Falls in Zambia or Zimbabwe, or in Cape Town (or other places) in South Africa, either of which will offer the potential for relaxing, whilst still enjoying a new and incredible experience.
If you are looking for a traditional beach destination to combine with Namibia, then many amazing beach locations can be comfortably reached via Johannesburg in South Africa, including Mozambique, Mauritius, and Seychelles.