I've travelled alone loads. If you want more detailed advice, can you be more specific about what sort of holiday are you after. You say 'simple pool/beach' holiday but that can cover anything from "all inclusive/never leave a large restort hotel" to "nice hotel in a location with a bit to do in terms of history and local restaurants'. If you literally don't want to leave your hotel then you will get different recommendations as to wanting a bit to do out of the hotel.
Some to things to think about are
Location and culture. Long /medium/short haul? (assuming you are in the UK) Some places are very easy to travel as a woman alone others are more challenging. I'd avoid Morocco for a first trip alone as there is a lot of pestering. Some Caribbean islands/hotels can be a bit full on set up for couples which can be a bore if you are alone. That said, a friend did the body holiday in St Lucia and raved about it. The USA is fantastic for women travelling alone as culturally they are very welcoming and chatty if that's what you want but equally will leave you alone if you aren't.
Hotel. I don't like all-inclusive as I like trying out local cuisine and restaurants but some people love them as they don't want to move. Large chain hotels (thinking of Hilton, Hyatt, Marriot types) tend to have lots of business travelers so being alone woman is easy and not a big deal. Resort hotels can be purely set up for families and this can be less fun if you are a lone woman but depends on what you like to do. I like to have a glass of wine in the bar whilst I read a book but I enjoy an atmosphere and a bit of people watching. Some family type resorts the bar can be absolutely dead in the evening as the families have all done an early bird dinner.
Timing When are you thinking of going? Now? A major advantage of traveling alone is you can go anytime. shoulder seasons for your chosen location are usually great because it's cheaper, no families as outside school holidays and tend to be quieter which makes for a relaxing holiday.
What's your budget?
PS: LOL at the unhelpful person who said they couldn't even go to a restaurant alone. What is the point of posting that? The OP was asking for advice not for your to waste their time with your own fears and weaknesses!