Fix, pay off mortgage completely or offset?

getmore4less

2. that just messes with the 50:50 probably best to try to avoid complicating the equity.

3. Barclays allow ISA offset so you can continue to build up your ISA and convert it to S&S later.

How much surplus cash are you generating between you, might be better to carry on with the cheapest mortgage you can get and keep saving/investing maxing out ISA first.
If 40% tax payers more pension is an option

Emergency funds don't need to be that big just enough to cover a big bill and if you have a healthy income surplus you can just stop saving to cover emergencies.

The disaster fund for loss of income that needs to be a few months expenses does not need to be instant access just accessible even if you lose a bit of interest it not a big deal that means you can look for a product for your joint funds.

if you want a long read on offsets here is the old numbers thread.
https://forums.moneysavingexpert.com/discussion/471

for the offset/savings question

the equation starts as
M : mortgage debt
S : standard rate
O : offset rate

C : savings capital
N : net savings rate

(M*S) - (C*N) == (M-C)*O

which simplified is

C(O-N) == M(O-S)

which become a simple ratio check of the mortgage saving against the rate differential

C/M == (O-S)/(O-N)

As said FD have one of the better offsets but you need to check if you qualify.
Also their rates are not that good these days on the offsets the differential on the 2y fix is 0.5% which is quite high.

for your £30k on £120k and offset rate of 2.14%(60% LTV) and 0.5% differential
if you can get a net savings rate of 0.14%, better off saving
if you can build the offset pot up quickly the rate needed gets higher at £60k offset savings rate needed is 1.14

Barclays are no better similar rates and higher fees.

There are other providers that are worth checking.

It seems the good old days of offset trackers at base+<1% and low margins(they were at 0.2% a couple of years back) are over

I suspect you are going to be better of with a decent cheap deal and focus on getting the best from your savings unless the flexibility is really attractive.