Sounds like you may have already purchased the F1's and if so, this is a moot point- but I have both F1's and Jet Fins. The F1's are heavy, but not necessarily negatively buoyant. Certainly no where as negative as the Jet Fins, which is what you are really after to cure your issue. If you really love your current fins, another option is to stick with them and just add some ankle weights around your ankles. The 1.5 lb ones work nicely.
Haven't bought fins yet. So your saying the Jets are heavier? I guess I'm in for Jets then.