With the beds being less than one meter wide, there is not a lot of room for border plants. If possible, consider widening the beds slighly to provide more space for some border plants. Below is a list of options that could provide a lovely border around your roses.

• Buxus ‘Koreana’ - Although you’re looking for alternatives to Buxus, this variety stays much lower and more compact than many other Buxus types, making it suitable for tight borders.
• Chinese plumbago (Ceratostigma plumbaginoides) - A low-growing groundcover that forms a tidy edging, with brilliant blue star-shaped flowers in late summer.
• English Lavender 'Hidcote' (Lavandula angustifolia) – A compact lavender with violet-blue flower spikes above silver-grey foliage. Works well as a fragrant border plant.
• Green mondo grass (Ophiopogon japonica) – A very low, hardy edging plant with fine foliage. Small white flowers appear in summer, followed by black berries.
• Liriope, lily-turf (Liriope muscari) – A hardy edging plant with dark purple flower spikes followed by black berries. Ideal for defining garden beds. 

As with all plants, prepare the soil thoroughly before planting by adding Garden Time™ Compost to the existing soil and mixing it in well. These plants will be smaller than most shrubs you plant, so space individual plants approximately 130-150 mm. apart. Trim regularly to maintain a dense bush habit.