5 things that make a coverall great, and make your workforce want to wear them
They have to be fit for purpose
Coveralls are mostly worn to protect the wearer from 'hazardous' elements in the environment encountered in some activity. An employer may issue workwear coveralls after a risk assessment has taken place, or there is an accepted industry precedent or legislation already in place. In this case the coveralls provided should meet industry standards for the particular hazard, e.g. Flame retardancy, Visibility or Protection against harmful chemicals.
Coveralls may also be issued as part of a company uniform, where the function is more to align with a corporate look, than protect from any hazards. Check that the garment's materials meet applicable standards for the intended environment(s) e.g. CE or EN (or ISO)
They have to be comfortable to wear
The most important ingredient to this is the fabric. The fabric has to protect the wearer from the hazard, yet not be so uncomfortable to wear (e.g. hot), as to be impractical. There are some instances where the hazard is so great that the wearer must endure this, and is only able to wear the garment for short periods. Fortunately manufactures are working with material scientists in the production of hi-tech composite highly breathable materials, protecting the wearer from the hazard at a comfortable temperatures in harsh environments. Choose breathable cotton rich fabrics where possible.
The coveralls have to fit well, with room for movement, yet not too baggy. The positioning of the crotch (combined with a full length two way zip) so that it's easy to take a pee, without having to hunch your shoulders or half undress. The coveralls should be available in a good range of sizes and leg lengths. Be wary of international sizing and some countries where a large is actually a small in UK/US.
It seems to me that a lot of coveralls are designed to go over other clothing and not as the primary garment, which means their cut can sometimes can be too roomy. A coverall as a primary garment, will look much smarter and can have a more tailored tighter fit.
These garments have to be worn all day, so any small features that make this easier will be appreciate by the workforce.
A sturdy 2 way full length zip
Adjustability, e.g. waist, cuffs
Useful pockets e.g. mobile phone, rule, loop hammer, tools, trouser pocket access
Built-in Knee pads
Consider all the small feature that make wearing the coverall a great experience and not a frustrating one.
Style & Design (your workforce need to want to wear them)
In the UK is has been hard to get away from the blue collar baggy boilersuit look; there is a lot of resistance from the younger employees who think that coveralls aren't "cool" to wear. As a solution, companies have adopted the cargo pant/polo shirt combo. I think this is a great shame, as a well designed coverall is a much smarter looking and more practical garment.
The British tend not to be peacocks, so not standing out too much is the key, (apart from where hi-vis is mandatory), so more subtle colour combinations should be used in coverall designs. As an example a contrasting yoke in a strong primary colour is something to be avoided. Choose more subtle darker shades, keep company logos small.
Although it seems like a good idea, your workforce will object to wearing large advertising lettering on their backs.
Choose durable coverall fabrics that will maintain their look after laundering, especially in situations where there is a lot of soiling. There is nothing worse than the look of a workforce wearing grubby ripped coveralls. Stain resistant (e.g.Teflon) coated fabrics will repel dirt, look better for longer and generally increase the garments working lifespan.