I want to do this without having to remove/strip having to strip paint from the frame which is already flaking off slowly.
If you don't do the preparation work, your paint will fail in short order regardless of colour.
The old saying about Preparation being 99% of the work is absolutely true. New Paint will not stick to the frame if the old paint is between them and flaking off.
The process for a good paint finish would be to strip the bike of all components and wash all oils off. Then remove all the loose old paint, treat any rust and then sand any remaining well-adhered paint to add tooth as well as smoothing the transitions.
Only then can you start with primer coat on bare metal, then thin colour coats, and finally clear-coats on top. Remember to let each layer dry according to the manufacturer's instructions, and to lightly scuff each layer just before wiping down and applying the next coat. Fine/thin layers are your goal.
Once the last coat has had a week to harden then reassembly can commence.
Anything less is a waste of paint and your results will be sub-optimal.
If you haven't got the time for all this then consider a wrap instead. Tape will go on much quicker and will hold all the loose paint in place. Downside is tape wraps can accelerate rust by holding moisture against the frame. Last resort is simply buy a bike in the colour you desire.
The color of choice depends on your favorite color, since it is very hard to color match. It's not like a car where you can find the color code easily. Personally I like the blue/green dual color look; green/black also looks good.
If you spray over your slowly flaking paint, it can start to slowly flake again next year or so depending on how you expose it. (It even may last a long time too.) If you want to do it properly where the paint stays on for years and years, you need to prepare the frame, including stripping flaking paint.