Maybe it will be best to take advice from our straight friends, and not a gay guy, but here are some ideas for what is worth 
About toys:
- I would go for something like a Clitoral tongue vibrator
- Maybe some good vibrator like a “rabbit vibrator” nothing too big or hardcore…
- Why not a sexy lingerie?
- You could try a penis ring with clitoral vibrator?
Some Ideas:
- You could also play with senses, blindfold, a sensual massage… oils, hot and cold…
- You could also use language if she is into it, dirty talk, sexting… a bit of teasing
- Do it in a different place, in the shower, on the couch…
About the stamina… Honestly, think long term. If being out of shape is the main problem, get in shape, you don’t have to be a model or a gym bro, just some cardio, something that will 1. improve your stamina 2. improve your health 3. improve your attractiveness to your partner… Sure you can try other positions, but if you improve yourself you will improve any position… If you weightlift you will be able to carry her and “move her around”, if you do stretching you may be able to do positions that you can’t now… So… that’s my advise.