Hero, the Western side of Crete is glorious ... the scenery is stunning, Chania is considered by Greeks to be the 2nd most beautiful Old Town in Greece (bested only by Nafplio), and, unlike that long stretch east of Heraklion, it is not overwhelmed by miles of purpose-built beacheries for package tourism. In fact, in threads on Western Crete, you seldom see the use of that telltale word, "resort." This Fab onlline map -- http://www.explorecrete.com/crete-maps/images/Crete-eot.png -- (cllick & it gets huuuge) can help you to find various locations.
Given your criteria, a splendid place for you, just outside of Chania, http://www.ammoshotel.com Would have been ideal for you. a boutique place (30 rooms) with a noted Cretan chef, on the beach but also with a pool (unusual in W Crete)-- a top-level inn w. moderate prices. Location, near Galatas (see map) and just 10 mins to Chania Old town, via a local bus running on inland side. Alas you are VERY late in booking dream places like this, esp. in High season! This place, a few Km west of Ammos, Corinna Mare, http://www.corinna.gr may meet your standards & has more rooms, thus more chance that there will still be vacancies available.
Places with a lot of UK Charter & package-tourism that you might find not as alluring, similar to the E of Heraklion stretch, might be the beach "strip" from Kato Stalos to Gerani ... and East of Chani at Kalives & Almirida. All along the north part of the west coast, inland a few miles are some lovely villas etc, but there, a car would be needed.
REthymnon, as u probably know from looking at a map, has an "old Town" right on the water, like Chania (altho it is smaller, and I find it quite crowdy even at off-season). Its "plus" is that starting in Old Town and stretching east for several kms is a long sandy beach fronted by Many hotels. A lot of them have that "international" or "convention- ready" look, from their websites & exterior (I've never stayed in one so can only judge from outside). However I believe there are also smaller places if you check booking.com and use a filter for "Stars" size & other critieria. One nice plus for Rethymnon is that it's the hub of many enterprises that take you exploring, either on hikes through small villages, or through a nearby gorge (Mili, a green & lovely short "trench" to the sea), or boat excursions. IF corinna Mare is full, or doesn't suit, I'd suggest doing some thoughtful research in Rethymnon area. IF you plan to rent a car, there are some lovely seaside places (Not package-tourism) on the Akrotiri peninsula just above Chania (Hania). Good hunting -- but do not delay!