Hi! I'm not a modder but I was thinking about this and rather than paying someone to do it you could just install the mod Up And Down And All Around (https://www.curseforge.com/minecraft/mc-mods/up-and-down-and-all-around), and make a few command blocks that detect when a player gets near them and /give them a "Gravity Anchor" using another command block. (A Gravity Anchor is an item from the mod that changes a players gravity) and then you can remove it with command blocks too.