You can use slime blocks as an instant way down. (When landing on a slime block, hold your jump button (space bar) and it'll break your fall and prevent you from being trampolined.) I'm not sure about a way up, because a slime block isn't powerful enough to boost you up into your floating base. (120 blocks fall onto slime block ~ 50-75 blocks trampolined.) You can always cheat and do "/give [playername] command_block 1" and put it under your floating base so you can command it to teleport you up there.