I am no expert on these matters but if you sell a house and buy another you must take in to account Auctioneers fees, Solicitor fees and Stamp duty which can amount to a few thousand less funds for your new house.
Also you should aim to own your house (not rent) for retirement, if you have rent to pay in retirement it is a chunk out of your pension and taxable earnings.
Alternatively no mortgage and no rent, you would pay nothing so this is not taken as taxable earnings.
Hope I explained that clearly
apologies.