I haven’t been to Gambia but it is on my list.
If you prefer more of a western environment I would try South Africa or Kenya as everything is very westernised when it comes to shops, malls etc. There are places you wouldn’t venture in to at night or even during the day but if you have your wits and some good advice, those two countries are excellent. Tinder is very prevalent in South Africa.
You suggested a brothel or RLD and both of these are available in abundance in South Africa but the issue with that is that the cops are bent will intimidate to illicit a bribe if they catch you picking up a women or coming out of a brothel. Prostitution is illegal but hidden in plain sight. Plus it feels very transactional. In Eastern Cape, I was having to beat women off with a stick on a dating app. Women literally would be open to any arrangement including short term. All you had to do was arrange an Uber or pick them up as the majority couldn’t accommodate as they were students looking to earn some extra dosh.
I am aiming to see Gambia at the latest by next year but will report back. One thing with African women is that they wear their heart on their sleeve and you will know pretty easily if someone is into you.