As an IFA (independent Financial advisor) a very rough guide to mortgages is for every £1000 you wish to borrow it will cost you approx £6 per month baserd on a repayment mortgage. IT's only a rough guide but a ball park figure.
Also on a single income you will get a mortgage of approx 3.5 or 4 times your annual income at a push.
Deposits are preferable as this then opens up better mortgage rate deals etc.
You need to think wether you are staying put for a while, do you earn bonuses to overpay the mortgage, do you like having a fixed monthly outgoing etc.
Best option is to speak to an IFA or mortgage broker. Normally they will charge a fee for finding the best mortgage for you. The company i am will charge £250/300ish fee (the larger the mortgage the bigger the fee) for their advice but the new lender may also charge a fee on top of that.
Usually get some free valuation or legals in deals from lenders also.
Anything else let me know.
P.S Commission on mortgage is not really an issue these days as most just charge a flat fee.