select convert(nvarchar(255), 4343)

declare @MyNumber int
set @MyNumber = 123
select 'My number is ' + CAST(@MyNumber as nvarchar(20))

declare @MyNumber float
set @MyNumber = 123.45
select 'My number is ' + CAST(@MyNumber as nvarchar(max))

DECLARE @value DECIMAL(19,4) = 1505.5698
SELECT CONVERT(NVARCHAR, @value)        -->  1505.5698
SELECT FORMAT(@value, 'N2', 'en-us')    --> 1,505.57
SELECT FORMAT(@value, 'N2', 'de-de')    --> 1.505,57