There is little evidence that the poorer  countrywomen of Wales wore stays, corsets or any other form of constrictive bodice although some prints of fancy Welsh costumes show women with very narrow waists.

Trade directories record 2 stay makers in towns in Wales in 1822 (Pigot’s) and 9 in 1849 (Hunt’s).

References to stays
An alternative to stays was the jump, a short coat or jacket, worn by both men and women.
Torbuck, J.T., (editor), A collection of Welch travels and memoirs of Wales. London, 1742

One writer recorded that in 1774, women wore stays on Sundays.
Sir John Cullum, Tour Through Several Counties of England and Part of North Wales, 1774, Bury St Edmunds and West Suffolk Record Office, E2/44/2.1-2.3

Ann Williams, the daughter of a vicar of several parishes in mid-Cardiganshire recorded in her diary for several days in early July, 1796 ‘mending my stays. Mrs Lewis the Mantua maker here. Busy with Mrs Lewis. Making a Dimity stays. Finished Bess’s stays.’ A few days later she recorded ‘A new Dimity stays came to 4s.’
NLW MS 22269A

early 19th century
A very few of Henry Pyne’s early 19th century drawings show women wearing bodices that were strapped at the back, rather like stays, but no Welsh examples of anything like these are known from drawings or surviving examples.

Thomas Edwards, (Twm o’r Nant, 1739-1810), writing in 1806 thought that those of the lower orders who wore stays were foolish.
Thomas Edwards, Interlude neu Chwareyddiaeth yn Gosod Allan y Tri Chryfion Byd sef Cariad, Tylodi ac Angeu, (Merthyr, 1850), p. 12

William Sandys, who travelled through Wales in 1819, noted (and drew) a pair of stays in the village shop at Pontrhydfendigaid, run by a woman dressed in a bedgown.
Sandys, William, ‘Walk through South Wales in October, 1819’ NLW Cwrt Mawr MS393 C

Eliza Spurrett noted when visiting Llangollen in 1825 that ‘many of [the women] preferring ease to elegance discard that necessary part of an Englishwomen’s dress commonly called stays’.
Eliza Spurrett, The Record Office for Leicestershire, Leicester & Rutland, 7D542/1

An anonymous traveller of the 1830s noted that Welsh women ‘appear to wear no stays; and consequently the bust is entirely devoid of all compactness of figure’.
Anon (Pedestres), A Pedestrian Tour of Thirteen Hundred and Forty Seven Miles through Wales and England (1836), vol. II, p.3

Edwin Roberts, writing of the women of Merthyr in 1852 wrote: ‘… either the absence of stays … or slovenliness, or want of tact, gives [Welsh women] an appearance of personal neglect; so that a young woman who may be as perfect as a Vatican Venus has no more shape than a matron of fifty’ Edwin Roberts, A visit to the iron works and environs of Merthyr Tydfil in 1852. (1853), p.11