Stumbled on this free software to create bowl and hollow form shapes and didn't know where to put a link but this is entertaining and useful. Software to design a bowl or hollow form then print and cut out to make a template. We may not want a template for more than rough forming but it gets you started. Fun to doodle with the software and every once in awhile I make something I want to save. I struggle a little with the bottom shape and working with this and the 3-D model in the side pane should help me. Documentation is slim but with a search in help I found that you double click a spot to add a new point to move around and just drag a point out of the work area to get rid of it. Easiest to make a smoothly flowing form using the fewest possible points to define it so after getting a shape you like getting unnecessary points out of the way may smooth the lines. I haven't found a way to do sharp corners, I think you have to just put several points very close together, not hard with the zoom, or maybe make a design in several sections on different drawings. Not super sophisticated for free but with instant three dimensional imaging in the side pane it seems pretty fancy to this old CAD operator from the age of dinosaurs!
Sorry if this is already posted, I didn't find it in a search.