Having looked into this very issue last month, I chose Ikea Mobile so that I could choose a number I want which I have now ported to a SIM only deal on a phone I already had. You could do the same with a new contract and port the number across if you want. You just lose £10 to Ikea but small potatoes to choose a number you want. My mobile ends with 000.
As for forwarding, there are several methods. In the end I also went with Voipfone but considered Soho66 and some others. In the end, it was the customer service which swung it over a marginally cheaper cost elsewhere.
If I could have chosen the number I wanted and was prepared to be stuck with Orange (pocket phone) or Vodafone (one net express) then you end up with a landline on a mobile with no forwarding costs.
Stand alone landlines on a SIM card often charge for both inward and outward minutes, very similar to the very start of mobiles in the UK (and USA) when they looked to earn from both sides of the coin. I didn't like this approach though I will consider the Orange and Vodafone alternatives going forward.