New Bike Help Needed!

Looking to get a mountain bike (always looking for new bikes of course) but due to lack of space looking to get one to share with my good lady so we can ride together but then I can use it at times too.

The issue is that i am 6ft and she is about 5ft 6 - any advice on bikes that would fit the bill? My though was to get one that is perfect for her and just adjust the seat post for me (or get a longer one so we can have seperate saddles too (she will want comfort whereas I prefer pain of course))?

All help greatly appreciated!

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.