Accessing certain variable instances without making dedicated functions?

Question

So just as a back story to what I've done so far and what I want to achieve...

Currently I'm using a whole heap of singleton classes to pass my instances around which is going to become a very bad idea very soon as I'm looking into multithreading and have heard(more like read) that singletons can become evil and a huge problem when multithreading is involved.

In my main init class, I've got code that initialises an window, renderer and a surface (SDL2). I'm wanting to break the code down so that I've got a class that handles only the window code, same with the renderer and surface too.

I'm looking for ways (if they're possible) to make an instance of a variable which will hold say the primary window, and then be able to access said variable without using a dedicated function... e.g:

in the init function of window:

bool Window::init() {
    m_primaryWindow = SDL_CreateWindow(creation info here);

    if (!m_primaryWindow) {
        SDL_LogInfo(INFO, "Primary Window Created");
        return true;
    }
    else {
        SDL_LogCritical(CRITICAL, "Could Not Create Primary Window:\n%s", SDL_GetError());
        return false;
    }
};

As you can see, normal right? Well, say I create a Window class in Game I'd have to add a function such as:

SDL_Window* primaryWindow = window.getPrimaryWindow();

To get that instance. But that's not what I want! I want to create only one SDL_Window variable in Window and reference to that in a function that uses a string maybe? eg:

SDL_Window* Window::getWindow(std::string id);

so that in Game I could just init and show the window and then call the instance like:

Window m_window;
m_window.getWindow(primaryWindow);

so that I can use that instead of constantly creating SDL_Window* variables all over my code.

Same needs to be done with the renderer too!

EDIT:

Ok, so I've made the following changes and it works... but I can't access the values within the mapped structure:

Window.hpp

typedef struct {
    SDL_Window* window;
    const char* title;
    int width;
    int height;
    int flags;
} m_windowStruct;

typedef std::map<std::string, m_windowStruct*> m_windowMap;

Window.cpp

bool Window::init() {
    if (!createWindow("window creation variables here") {
        return true;
    }
    else {
        return false;
    }
};

bool Window::createWindow(std::string id, const char* title, int width, int height, int flags) {
    m_windowMap* windowMap;
    m_windowStruct windowData;

    windowData.window = SDL_CreateWindow(title, 
        SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
        width, height, flags);

    if (!windowData.window) {
        windowData.title = tile;
        windowData.width = width;
        windowData.height = height;
        windowData.flags = flags;
        windowMap->insert(m_windowMap::value_type(id, &windowData));
        SDL_LogInfo(INFO, "Window creation successful");
        return true;
    }
    else{
        return false;
    }
};

So I guess my question now is.. How would I grab the window pointer from the struct within the map?

(also as a side note, how would I then destroy the pointer once I'm finished?)