Hiya Matheous...
OK, got it... you want to have a garden path constructed of stone slabs with gravel infilling between the slabs and no gradients required. An *S* or other curvy shape would look lovely, meandering through your garden....
The desire line is the *S* shape, materials are stone slabs and gravel infill. All you need to work out is the width of the path - have a look at some slabs in your local garden centre and see if you like the look of some of them - will they work (in terms of colour etc) with your existing garden ? What sort of width are you thinking of ? I'd be looking for a metre wide at least, possibly wider if your garden is big.
Be open to suggestions, paths can be constructed from many different materials - stone slabs, precast concrete cobbles or setts (which don't look like concrete!) or even bricks laid on their sides, say in a herringbone pattern.
In terms of the laying of the path itself, since it will be having a (grassed) lawn on either side, you may wish to have the level of the path itself at a slightly lower height than the grass, so that when cutting the grass you don't accidentally hit the path construction (useful when using a flymo for example). However if you are planting a border alongside the path edge, you won't need to worry about mowing the grass....
One small word of warning about a gravel infill - keep it to a minimum if you can or you may find your local kitties using the gravel as their fabby new high tech toilet.... (I kid you not, cats love gravel for that reason...)