Wanting an ND filter for 18-55mm Nikon lens.

Hey. I’ve been taking photos on my iPad for 5 years, and I only recently made a step up to a camera everyone told me ‘you need to start using a proper camera’. I have a Nikon D5200 with a 18-55mm lens and a 55-300mm lens (which I don’t use as much). The thing about my iPad, is that I have an app that allows me to take long exposures, in a range of conditions, including broad daylight. I have been very disappointed to find out that even in the fastest shutter speed, the lowest iso and the lowest exposure, and the smallest aperture, I can’t get a long exposure for even 3 seconds whiteout the image being completely white. I remember being on a trip on the Great Ocean Road when I found this out, so I asked somebody else who looked like they knew what they were doing with their camera, and he said that I’ll need a filter. I am looking to do this quite often... shoot long exposure in broad daylight. Anyway, after doing some research, I found that the best filter is an ND filter, maybe 10 stops (let me know if there’s a better one), but I wanted to check with all of you first. What sized NV filter with 10 stops will fit onto a 18-55mm lens if there is one? Is there a better filter that will darken my photos more, or just has an overall better effect? (not too fussed about nice colour effects though, because I can always edit in Lightroom. It’s just the overexposed white long exposures that are too much to be restored in Lightroom). Is there anything that I’m not considering? I don’t want to invest in this and then be disappointed, as I don’t currently have a job and can’t afford to buy something that turns out to not work and do what I’d hoped.  I want to find a filter that will do exactly what I want without wasting money.

thoughts?