Have you tried BIMP?

It has an option to do exactly what you need! In Resize dialogue window >> Set_exact_size_in_pixel >> Set_height_only (730 or whatever you need). Width setting will become greyed out, because plugin will resize all your images with varying sizes preserving aspect ratio. Or set fixed Width for all images. I've just tested BIMP on 50 arbitrary images with different dimensions and it did a great job at keeping aspect ratio. All images came out of exact H but different W's (or desired W and different H). Not only that - it keeps your current image formats (jpg, bmp, png etc) resizing at best compression, optimization etc. rates to preserve the images quality. Just try it already :)