Next step on the ladder.. Save or pay off existing mortgage?

Whoknowskt89

Hi all!
I'm 3 pay days away from being debt free and wondering how best to go around selling my flat and buying a freehold house.

I've got just shy of 3 years left on my fixed mortgage, currently just shy of £68k remaining. My regular payments are £328.81 but I overpay as I didn't like the odd figure (£340 so not much but all helps)

Flat worth: £110k
Mortgage: £68k
Equity: £42k
Mortgage: 3.75% fixed until 31/12/2019, 10% overpayments allowed a year without fees

I'm looking at moving out of the area I'm in and houses I'm looking at vary between £140k and £195k though I don't think I'll quite manage the top end!

Once my debt is gone, I'm looking at saving between £400 and £600 a month and wondering what is best. I know I'll need money for solicitors, estate agents, moving costs etc.

Should I split it so that:
£100 extra to mortgage every month
Rest to savings

Or all to savings

Or another option I haven't thought about?

I'm currently on £29k, I'm 27 and have a decent work pension scheme. Looking to move sometime after 2020. Live alone with 4 cats and who knows how many tropical fish!

Thanks

Any advice would be highly appreciated!