Hi wowfudge
I have no idea about Newton Leys - is that the new housing development? Personally I would avoid Bletchley as I prefer somewhere with an identifiable town centre & high street. I'm not sure if Bletchley has this. It's certainly got amenities including smart looking leisure centre tho' I've not been there. There are lots of big DIY 'sheds' there, Ikea & ASDA & the Stadium MK has a new Odeon IMAX next door to it, plus parade of restaurants (Pizza Express, Frankie & Bennies, Chimichanga etc), and a shopping 'centre' - Primark, Next, BHS, Top Shop, M&S. Bletchley Park is a great place to visit if you're into coding & WW2 stuff!
If you want a small town, then I know Leighton Buzzard/Linslade a bit, which is 10 mins south of Newton Leys. Linslade is the area to the west of the Grand Union Canal, Leighton Buzzard is to the east and is where the town centre is.
There's a fast train service to Euston (35 mins), station is about 20 mins walk maximum from Linslade side of town, but may be a lot further if you live on the Leighton Buzzard side, particularly if you go as far out as Heath Reach. LB is a small market town with a pretty good high street, twice weekly market, small Waitrose, big Tesco & Morrisons, WHSmith, Boots, Costa, Halfords, local specialist shops & cafes, local butcher, Pizza Express, some good pubs (esp The Black Lion), town centre park with a bandstand & splash & play park, canal towpath is nice for walks, lots of green space / country parks / woods around the town, golf club. It's 15 mins in the train or 20 mins drive to MK shopping centre or MK Stadium. There's a leisure centre with fitness gym & pool in LB, run by the local authority, which has just had a bit of a refurb.
Hope that helps a bit! Good luck 