Jumbo is the other chain I've found, variable service experiences (personal boo to Zurich, yay to Luzern staff).
Bauhaus has some sites in Swissy (not so many of these in this country, but plenty in Germany) and the Leroy Merlins just over the borders of France and Italy are very good too.
Obi is the other group of stores, don't seem to be many of these, but their stuff is higher end for quality and price, than the usual big box stores, but again, they've got a wide range.
Fairly easy to setup email alerts or get their catalogues delivered, but I've found that the individual stores also seem to have the power to slash prices as they see fit. All of the above do spectacular discounts from time to time (I've seen a Jacuzzi spa from 12,000 down to 3,000; indoor light fittings in perfect nick at 70% discount, established trees from 40 down to 5 etc - and they're genuine discounts, rather than the mark up to make it look marked down)
All of the above usually also have a spot in the store where they've got a stash of heavily discounted stock - usually discontinued or damaged stuff. Interestingly, they all seem to have seasonal discounts happen before the season (eg: sales on Christmas lights happen in October/November, snow clearing machines on sale in September/October). There are the usual post season sales too, but only on very select things (I thought I'd snap up a tonne of Christmas lights December 28th, but nope, the stock had been taken off shelves December 24th. I had my choice of bounce to music snowmen though!)
The Landi chain has some useful odds and sods for DIY as well - geared more for farmers and gardeners, but worth a look as they sell a good range of wines at stupidly good prices.
Haven't found anywhere in Swissy where paint is a respectable price though - not at the big box stores or at the specialist stores. Would love to hear from anyone who has found a source?
Also haven't found a source for topsoil, other than in bags at the Landi or in the other stores mentioned above. I'd really like to tow the trailer somewhere and have it filled up with dirt/gravel/manure fertiliser/stones etc rather than buying lots and lots of bags of the stuff. Talking to my Swissy neighbours, it appears to be common practice to have a landscaping company do all that kind of graft rather than getting access to the materials and DIYing it? Would love any advice here...
Happy shopping!