When I was using my vintage machine I found I couldn't do much in the middle of a queen sized quilt, and so I typically used various types of grids and gentle curves and then did something fancier around the border. Orange peel and clam shell would be example of doable curves. Pumpkin seed slightly fancier but nice border for an orange peel center.
Keep in mind the ideas of echoing and repeating and multiple passes, so you can have a chain of squares that takes a little more effort, but then you can echo that with a zig zag (slightly easier) and then straight lines on either side of that. Then you can separate out and either introduce a different design element or keep repeating the original set.